Support CPM_SOURCE_CACHE on windows (#109)

* use semicolon as empty command and add test

* remove platform specific test coverage

* only run actions for pushes and prs into master (avoid duplication)

* remove cache test as it's already part of the test suite

* update version

* test cache reuse

.github/workflows/macos.yml

@@ -1,11 +1,17 @@
 name: MacOS
 
-on: [push]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
 
 jobs:
   build:
 
-    runs-on: macOS-10.14
+    runs-on: macos-latest
     
     steps:
     - uses: actions/checkout@v1

.github/workflows/ubuntu.yml

@@ -1,11 +1,17 @@
 name: Ubuntu
 
-on: [push]
+on:
+  push:
+    branches:
+    - master
+  pull_request:
+    branches:
+    - master
 
 jobs:
   build:
 
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     
     steps:
     - uses: actions/checkout@v1

.github/workflows/windows.yml

@@ -1,11 +1,17 @@
 name: Windows
 
-on: [push]
+on:
+  push:
+    branches:
+    - master
+  pull_request:
+    branches:
+    - master
 
 jobs:
   build:
 
-    runs-on: windows-2019
+    runs-on: windows-latest
     
     steps:
     - uses: actions/checkout@v1