Bump the PyDSDL version number

This is a tentative fix. A proper long-term solution is described in #68.

.travis.yml

@@ -2,6 +2,6 @@ language: python
 python:
   - "3.6"
 before_install:
-  - pip install pydsdl~=1.1
+  - pip install pydsdl~=1.2
 script:
   - ./test.py