Rust 1.50 fixes (#2199)

## Issue Addressed

https://rustsec.org/advisories/RUSTSEC-2021-0021.html

## Proposed Changes

* Bump `nb-connect` to avoid the above advisory (and migrate from the yanked crate)
* Add a `rustup update stable` to the Docker build to fix this issue: https://github.com/sigp/lighthouse/actions/runs/567075245

.github/workflows/docker.yml

@@ -28,6 +28,8 @@ jobs:
             DOCKER_CLI_EXPERIMENTAL: enabled
         steps:
             - uses: actions/checkout@v2
+            - name: Update Rust
+              run: rustup update stable
             - name: Dockerhub login
               run: |
                   echo "${DOCKER_PASSWORD}" | docker login --username ${DOCKER_USERNAME} --password-stdin
@@ -58,6 +60,8 @@ jobs:
         needs: [extract-branch-name]
         steps:
             - uses: actions/checkout@v2
+            - name: Update Rust
+              run: rustup update stable
             - name: Dockerhub login
               run: |
                   echo "${DOCKER_PASSWORD}" | docker login --username ${DOCKER_USERNAME} --password-stdin

Cargo.lock

@@ -4045,12 +4045,12 @@ dependencies = [
 
 [[package]]
 name = "nb-connect"
-version = "1.0.2"
+version = "1.0.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8123a81538e457d44b933a02faf885d3fe8408806b23fa700e8f01c6c3a98998"
+checksum = "670361df1bc2399ee1ff50406a0d422587dd3bb0da596e1978fe8e05dabddf4f"
 dependencies = [
  "libc",
- "winapi 0.3.9",
+ "socket2",
 ]
 
 [[package]]