Add gradle wrapper validation (#53)

Author: mattmook

.github/workflows/gradle-wrapper-validation.yml

@@ -0,0 +1,19 @@
+name: "Validate Gradle Wrapper"
+
+on:
+  push:
+    branches:
+    - master
+    tags:
+    - '*'
+  pull_request:
+    branches:
+    - master
+
+jobs:
+  validation:
+    name: "Validation"
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: gradle/wrapper-validation-action@v1