ci: add java 7 in the test matrix

It was already present in the Travis test matrix.

Author: darrachequesne

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
 
     strategy:
       matrix:
-        java: [8, 11]
+        java: [7, 8, 11]
 
     steps:
       - uses: actions/checkout@v2