Update cmake.yml

.github/workflows/cmake.yml

@@ -20,6 +20,12 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
+    
+    - name: Install system dependencies
+      if: runner.os == 'Linux'
+      run: |
+        sudo apt-get update
+        sudo apt-get -y install libgtk-3-dev
 
     - name: Configure CMake
       # Configure CMake in a 'build' subdirectory. `CMAKE_BUILD_TYPE` is only required if you are using a single-configuration generator such as make.