Update GitHub actions/checkout to v2 (#10496)

Author: eksperimental

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
             development: true
     runs-on: ubuntu-16.04
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
         with:
           fetch-depth: 50
       - name: Install Erlang/OTP
@@ -33,7 +33,7 @@ jobs:
           mkdir -p otp
           tar zxf otp.tar.gz -C otp --strip-components=1
           otp/Install -minimal $(pwd)/otp
-          echo "::add-path::$(pwd)/otp/bin"
+          echo "$(pwd)/otp/bin" >> $GITHUB_PATH
       - name: Compile Elixir
         run: |
           rm -rf .git
@@ -61,7 +61,7 @@ jobs:
     steps:
       - name: Configure Git
         run: git config --global core.autocrlf input
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
         with:
           fetch-depth: 50
       - name: Cache Erlang/OTP package
@@ -88,7 +88,7 @@ jobs:
     name: Check POSIX-compliant
     runs-on: ubuntu-16.04
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
         with:
           fetch-depth: 50
       - name: Install Shellcheck