Update pytest dependency. Replace py.test references with pytest.

Author: geowurster

Diff for: .travis.yml

@@ -18,7 +18,7 @@ install:
   - pip install -e .\[dev\]
 
 script:
-  - py.test tests --cov click_plugins --cov-report term-missing
+  - pytest tests --cov click_plugins --cov-report term-missing
 
 after_success:
   - coveralls

Diff for: README.rst

@@ -165,7 +165,7 @@ Developing
     $ git clone https://github.com/click-contrib/click-plugins.git
     $ cd click-plugins
     $ pip install -e .\[dev\]
-    $ py.test tests --cov click_plugins --cov-report term-missing
+    $ pytest tests --cov click_plugins --cov-report term-missing
 
 
 Changelog

Diff for: setup.py

@@ -51,7 +51,7 @@
                 "via setuptools entry-points.",
     extras_require={
         'dev': [
-            'pytest',
+            'pytest>=3',
             'pytest-cov',
             'wheel',
             'coveralls'