Bump back to 1.50.0 due to unstable library feature unsafe_cell_get_mut in state library

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       matrix:
         include:
           - { rust: stable, os: ubuntu-latest }
-          - { rust: 1.49.0, os: ubuntu-latest }
+          - { rust: 1.50.0, os: ubuntu-latest }
     steps:
       - name: Checkout
         uses: actions/checkout@v2

README.md

@@ -34,7 +34,7 @@
 * [Docs](https://docs.rs/async-graphql)
 * [GitHub repository](https://github.com/async-graphql/async-graphql)
 * [Cargo package](https://crates.io/crates/async-graphql)
-* Minimum supported Rust version: 1.49.0 or later
+* Minimum supported Rust version: 1.50.0 or later
 
 ## Safety