Build on all supported platforms (#139)

* Build on all supported platforms

* rename job

.github/workflows/build.yml

@@ -8,14 +8,16 @@ on:
 
 jobs:
   build:
-    name: Build on ${{ matrix.os }} / Node.js v${{ matrix.nodejs }}
+    name: Build
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
         os:
-        - Windows-latest
-        - macOS-latest
-        - Ubuntu-latest
+        - Windows-2019
+        - macOS-10.15
+        - Ubuntu-16.04
+        - Ubuntu-18.04
+        - Ubuntu-20.04
         nodejs:
         - 12
       fail-fast: false