Migrate from Travis to GitHub Actions (#114)

Add two actions: One to build the app, another to validate the checksums
of the Gradle Wrapper files.

Author: drewhannay

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

@@ -0,0 +1,17 @@
+name: "Validate Gradle Wrapper"
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - '*'
+
+jobs:
+  validation:
+    name: "Validation"
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: gradle/wrapper-validation-action@v1
+

.github/workflows/merge-check.yml

@@ -0,0 +1,31 @@
+name: Merge checks
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - '*'
+
+jobs:
+  build:
+    name: Build project
+    runs-on: ubuntu-latest
+    if: ${{ !contains(github.event.head_commit.message, 'ci skip') }}
+    steps:
+      - name: Checkout Repo
+        uses: actions/checkout@v2
+
+      - name: Cache Gradle Files
+        uses: actions/cache@v2
+        with:
+          path: |
+            ~/.gradle/caches/
+            ~/.gradle/wrapper/
+          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}
+          restore-keys: |
+            ${{ runner.os }}-gradle-
+
+      - name: Run Gradle tasks
+        run: ./gradlew build

.travis.yml

@@ -1,4 +1,4 @@
-Spyglass [![Build Status](https://travis-ci.org/linkedin/Spyglass.svg?branch=master)](https://travis-ci.org/linkedin/Spyglass)
+Spyglass [![Build Status](https://img.shields.io/github/workflow/status/linkedin/Spyglass/Merge%20checks)](https://img.shields.io/github/workflow/status/linkedin/Spyglass/Merge%20checks)
 ========
 
 A powerful Android library that provides highly-customizable widgets (with smart defaults) to easily add social-media-esque mention (aka tag) support to your app