test: Use Github Actions instead of travis.ci

It's easy to use Github Actions to test on multiple OSs and multiple
versions of Qt, so use it instead of travis.ci.

SingleApplication submodule URL is also modified in this commit, please
change it back after itay-grudev/SingleApplication#90 is merged.

.github/workflows/test.yml

@@ -0,0 +1,30 @@
+name: "CI: Build Test"
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    strategy:
+      matrix:
+        qt_version: [5.12.0, 5.12.6, 5.14.0]
+        platform: [ubuntu-latest, windows-latest, macos-latest]
+
+    runs-on: ${{ matrix.platform }}
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Install Qt
+      uses: jurplel/[email protected]
+      with:
+        version: ${{ matrix.qt_version }}
+
+    - name: get submodules
+      run: git submodule update --init --recursive
+
+    - name: cmake
+      run: cmake .
+
+    - name: cmake build
+      run: cmake --build .

.gitmodules

@@ -3,4 +3,4 @@
 	url = https://github.com/ouuan/QCodeEditor.git
 [submodule "third_party/singleapplication"]
 	path = third_party/singleapplication
-	url = https://github.com/itay-grudev/SingleApplication.git
+	url = https://github.com/ouuan/SingleApplication.git

README.md

@@ -1,6 +1,6 @@
 # CP Editor
 
-[![Build Status](https://travis-ci.org/ouuan/cp-editor.svg?branch=master)](https://travis-ci.org/ouuan/cp-editor)
+[![CI: Build Test](https://github.com/ouuan/cp-editor/workflows/CI:%20Build%20Test/badge.svg)](https://github.com/ouuan/cp-editor/actions)
 [![Latest Stable](https://img.shields.io/github/v/release/coder3101/cp-editor?label=latest%20stable)](https://github.com/coder3101/cp-editor/releases/latest)
 [![Latest Release](https://img.shields.io/github/v/release/coder3101/cp-editor?include_prereleases&label=latest%20release&sort=semver)](https://github.com/coder3101/cp-editor/releases)