Add explicit support for Python 3.7 and 3.8

Author: jaywhy13

.travis.yml

@@ -5,6 +5,8 @@ python:
   - "3.4"
   - "3.5"
   - "3.6"
+  - "3.7"
+  - "3.8"
   - "nightly"
   - "pypy"
 

setup.py

@@ -22,7 +22,7 @@
     "mock",
     "pytest>=3.0.0",
     "pytest-cov",
-    "pytest-mock",
+    "pytest-mock<3.0.0",
     "pytz",
     "coverage<5.0.0"
 ]
@@ -53,6 +53,8 @@
         "Programming Language :: Python :: 3.4",
         "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
+        "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: Implementation :: CPython",
         "Programming Language :: Python :: Implementation :: PyPy",
     ],