Update travis.yml, add .gitignore

Author: aparajita

.gitignore

@@ -0,0 +1 @@
+.DS_Store

.travis.yml

@@ -7,5 +7,5 @@ install:
   - pip install pep257
 # command to run tests
 script:
-  - flake8 . --max-line-length=120
-  - pep257 .
+  - flake8 . --max-line-length=120 --exclude=__init__.py,linter-plugin-template
+  - pep257 . --ignore=D202