Work around Travis' bad matrix expansion bugs

Author: zbeekman

.travis.yml

@@ -13,12 +13,21 @@ env:
     - MPICH_GCC7_BOT_URL_HEAD="https://github.com/sourceryinstitute/OpenCoarrays/files/976779/"
     - MPICH_BOT_URL_TAIL="mpich-3.2_3.yosemite.bottle.1.tar.gz"
     - BUILD_TYPES="Release Debug RelWithDebInfo CodeCoverage"
-  matrix:
-    - GCC="6 7" OSX_PACKAGES="shellcheck gcc gcc@6 cmake" BUILD_TYPE="cmake"
-    - GCC="6" OSX_PACKAGES="shellcheck gcc@6 cmake" BUILD_TYPE="InstallScript"
 
 matrix:
   fast_finish: true
+    -
+      os: osx
+      env:
+        - GCC="6 7"
+          OSX_PACKAGES="shellcheck gcc gcc@6 cmake"
+          BUILD_TYPE="cmake"
+    -
+      os: osx
+      env:
+        - BUILD_TYPE="InstallScript"
+          OSX_PACKAGES="shellcheck gcc@6"
+          GCC=6
     - &ubuntu
       os: linux
       sudo: false