[travis] Reduce osx builds to one

Author: mpsonntag

.travis.yml

@@ -4,23 +4,26 @@ dist: trusty
 language: python
 
 matrix:
-    include:
-        - os: linux
-          python: "2.7"
-          env: COVERALLS=1
-        - os: linux
-          python: "3.4"
-        - os: linux
-          python: "3.5"
+  include:
+    - os: linux
+      python: "2.7"
+      env: COVERALLS=1
+    - os: linux
+      python: "3.4"
+    - os: linux
+      python: "3.5"
 
-        - os: osx
-          language: generic
-          env:
-            - OSXENV=2.7
-        - os: osx
-          language: generic
-          env:
-            - OSXENV=3.5
+    - os: osx
+      language: generic
+      env:
+        - OSXENV=3.5
+#    Keep only one osx branch active for now
+#    since currently osx builds on travis
+#    are frequently stalled or indefinitely delayed.
+#    - os: osx
+#      language: generic
+#      env:
+#        - OSXENV=2.7
 
 before_install:
   - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then bash resources/install_osx_virtualenv.sh; fi