Update codeql-analysis.yml (#209)

* Update codeql-analysis.yml

.github/workflows/codeql-analysis.yml

@@ -9,7 +9,7 @@ on:
 jobs:
   CodeQL-Build:
 
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
 
     steps:
     - name: Checkout repository
@@ -19,11 +19,11 @@ jobs:
         # a pull request then we can checkout the head.
         fetch-depth: 2
 
-    # If this run was triggered by a pull request event, then checkout
-    # the head of the pull request instead of the merge commit.
-    - run: git checkout HEAD^2
-      if: ${{ github.event_name == 'pull_request' }}
-      
+    - name: Set up JDK
+      uses: actions/setup-java@v1
+      with:
+        java-version: 8
+
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL
       uses: github/codeql-action/init@v1