don't img test on python 3.6

Author: phobson

.travis.yml

@@ -14,19 +14,14 @@ matrix:
         - ARGS="--mpl --verbose"
     - python: 3.5
       env:
-        - COVERAGE=false
+        - COVERAGE=true
         - EXTRATESTERS=""
         - ARGS="--mpl --verbose"
     - python: 3.6
       env:
         - COVERAGE=false
         - EXTRATESTERS=""
-        - ARGS="--mpl --verbose"
-    - python: 3.6
-      env:
-        - COVERAGE=true
-        - EXTRATESTERS=""
-        - ARGS="--mpl --verbose --pep8"
+        - ARGS="--verbose --pep8"
 
 before_install: