Downgrade tokio to avoid run-time error

```
thread 'main' panicked at 'there is no reactor running, must be called from the context of Tokio runtime', ~/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-0.2.22/src/io/driver/mod.rs:201:9
```

Cargo.lock

@@ -538,7 +538,7 @@ dependencies = [
  "http",
  "indexmap",
  "slab",
- "tokio 0.2.22",
+ "tokio",
  "tokio-util",
  "tracing",
  "tracing-futures",
@@ -674,7 +674,7 @@ dependencies = [
  "itoa",
  "pin-project 1.0.1",
  "socket2",
- "tokio 0.2.22",
+ "tokio",
  "tower-service",
  "tracing",
  "want",
@@ -825,12 +825,35 @@ dependencies = [
  "kernel32-sys",
  "libc",
  "log",
- "miow",
+ "miow 0.2.1",
  "net2",
  "slab",
  "winapi 0.2.8",
 ]
 
+[[package]]
+name = "mio-named-pipes"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0840c1c50fd55e521b247f949c241c9997709f23bd7f023b9762cd561e935656"
+dependencies = [
+ "log",
+ "mio",
+ "miow 0.3.5",
+ "winapi 0.3.9",
+]
+
+[[package]]
+name = "mio-uds"
+version = "0.6.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "afcb699eb26d4332647cc848492bbc15eafb26f08d0304550d5aa1f612e066f0"
+dependencies = [
+ "iovec",
+ "libc",
+ "mio",
+]
+
 [[package]]
 name = "miow"
 version = "0.2.1"
@@ -843,6 +866,16 @@ dependencies = [
  "ws2_32-sys",
 ]
 
+[[package]]
+name = "miow"
+version = "0.3.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "07b88fb9795d4d36d62a012dfbf49a8f5cf12751f36d31a9dbe66d528e58979e"
+dependencies = [
+ "socket2",
+ "winapi 0.3.9",
+]
+
 [[package]]
 name = "net2"
 version = "0.2.35"
@@ -1004,7 +1037,7 @@ dependencies = [
  "serde_json",
  "sha2",
  "structopt",
- "tokio 0.3.3",
+ "tokio",
  "warp",
 ]
 
@@ -1390,6 +1423,15 @@ dependencies = [
  "opaque-debug 0.3.0",
 ]
 
+[[package]]
+name = "signal-hook-registry"
+version = "1.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ce32ea0c6c56d5eacaeb814fbed9960547021d3edd010ded1425f180536b20ab"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "siphasher"
 version = "0.3.3"
@@ -1558,30 +1600,24 @@ dependencies = [
  "futures-core",
  "iovec",
  "lazy_static",
+ "libc",
  "memchr",
  "mio",
- "pin-project-lite",
- "slab",
-]
-
-[[package]]
-name = "tokio"
-version = "0.3.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e5ca08accbcb46f11fd8d2d1c6158c348b7888009a1f39260bcad66f6a454250"
-dependencies = [
- "autocfg",
+ "mio-named-pipes",
+ "mio-uds",
  "num_cpus",
  "pin-project-lite",
+ "signal-hook-registry",
  "slab",
  "tokio-macros",
+ "winapi 0.3.9",
 ]
 
 [[package]]
 name = "tokio-macros"
-version = "0.3.1"
+version = "0.2.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "21d30fdbb5dc2d8f91049691aa1a9d4d4ae422a21c334ce8936e5886d30c5c45"
+checksum = "f0c3acc6aa564495a0f2e1d59fab677cd7f81a19994cfc7f3ad0e64301560389"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1596,7 +1632,7 @@ checksum = "e12831b255bcfa39dc0436b01e19fea231a37db570686c06ee72c423479f889a"
 dependencies = [
  "futures-core",
  "rustls",
- "tokio 0.2.22",
+ "tokio",
  "webpki",
 ]
 
@@ -1611,7 +1647,7 @@ dependencies = [
  "futures-sink",
  "log",
  "pin-project-lite",
- "tokio 0.2.22",
+ "tokio",
 ]
 
 [[package]]
@@ -1808,7 +1844,7 @@ dependencies = [
  "serde",
  "serde_json",
  "serde_urlencoded",
- "tokio 0.2.22",
+ "tokio",
  "tokio-rustls",
  "tower-service",
  "tracing",

Cargo.toml

@@ -28,7 +28,7 @@ serde = { version = "1.0.117", features = ["derive"] }
 serde_json = "1.0.59"
 sha2 = "0.9.1"
 structopt = { version = "0.3.20", features = ["color"] }
-tokio = { version = "0.3.3", features = ["macros", "rt", "rt-multi-thread"] }
+tokio = { version = "0.2.22", features = ["full"] }
 warp = { version = "0.2.5", default-features = false, features = ["tls"] }
 
 [dev-dependencies]