fix typo submodule -> submodules

Author: kateinoigakukun

.github/workflows/test.yml

@@ -14,7 +14,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
         with:
-          submodule: true
+          submodules: true
       - name: Setup swiftenv
         run: |
           git clone https://github.com/kylef/swiftenv.git ~/.swiftenv
@@ -36,7 +36,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
         with:
-          submodule: true
+          submodules: true
       - run: sudo xcode-select -s "${{ matrix.xcode-version }}"
       - run: swift --version
       - run: swift test
@@ -46,7 +46,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
         with:
-          submodule: true
+          submodules: true
       - run: swift test --enable-code-coverage
       - run: echo "SWIFT_CODECOV_PATH=$(swift test --show-codecov-path)" >> $GITHUB_ENV
       - uses: codecov/codecov-action@v1