Removed problem versions from travis-ci file

.travis.yml

@@ -2,9 +2,9 @@ language: python
 python:
   - "2.7"
   - "3.6"
-  - "3.6-dev" # 3.6 development branch
-  - "3.7-dev" # 3.7 development branch
-  - "nightly" # currently points to 3.7-dev
+#  - "3.6-dev" # 3.6 development branch
+#  - "3.7-dev" # 3.7 development branch
+#  - "nightly" # currently points to 3.7-dev
 # command to install Ubuntu packages before installing
 before_install:
   - sudo apt-get update -qq