Add composer to phpunit build step

Author: jpresutti

.github/workflows/PhpUnit.yaml

@@ -14,6 +14,20 @@ jobs:
           extensions: bcmath
           coverage: xdebug
           tools: phpunit
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+          restore-keys: ${{ runner.os }}-composer-
+
+      - name: Install dependencies
+        run: composer install --prefer-dist
+
       - name: Run PHPUnit
         run: phpunit -c tests/githubphpunit.xml --coverage-clover coverage.xml
       - uses: codecov/codecov-action@v1