updated workflow

.github/workflows/build.yml

@@ -9,10 +9,9 @@ jobs:
 
     strategy:
       matrix:
-        os: [ubuntu-18.04]
         compiler: [g++, clang++]
 
-    runs-on: ${{ matrix.os }}
+    runs-on: ubuntu-latest
 
     steps:
     - uses: actions/checkout@v1
@@ -34,14 +33,9 @@ jobs:
 
     strategy:
       matrix:
-        os: [windows-2019, windows-2016]
-        include:
-          - os: windows-2019
-            generator: Visual Studio 16 2019
-          - os: windows-2016
-            generator: Visual Studio 15 2017
+        generator: [Visual Studio 16 2019]
 
-    runs-on: ${{ matrix.os }}
+    runs-on: windows-latest
 
     steps:
     - uses: actions/checkout@v1
@@ -58,7 +52,7 @@ jobs:
 
   macos:
     timeout-minutes: 5
-    runs-on: macOS-10.14
+    runs-on: macOS-latest
 
     steps:
     - uses: actions/checkout@v1