Merge pull request #155 from cclauss/patch-3

pip install pycocotools is broken in Travis CI

.travis.yml

+group: travis_latest
+language: python
+cache: pip
+python:
+    - 2.7
+    - 3.6
+install:
+    - pip install --upgrade pip 
+    - pip install pycocotools
+script:
+    - true