Travis CI: Disable macOS checks - no longer available

Author: HenrikBengtsson

.travis.yml

@@ -30,10 +30,10 @@ matrix:
         - _R_CHECK_LENGTH_1_CONDITION_=true
         - _R_CHECK_LENGTH_1_LOGIC2_=true
         - _R_CLASS_MATRIX_ARRAY_=true
-    - os: osx
-      r: oldrel
-    - os: osx
-      r: release
+#    - os: osx
+#      r: oldrel
+#    - os: osx
+#      r: release
     - os: linux
       r: release
       r_check_args: --no-build-vignettes --no-codoc --no-examples --no-tests --no-manual --ignore-vignettes