Pin pymongo version

This will mitigate issue pandas-dev#397 temporarily

Author: kraphtuos

.travis.yml

@@ -22,7 +22,7 @@ install:
   - pip install python-dateutil --upgrade
   - pip install pytz --upgrade
   - pip install tzlocal --upgrade
-  - pip install pymongo --upgrade
+  - pip install pymongo==3.4.0
   - pip install numpy --upgrade
   - pip install pandas --upgrade
   - pip install decorator --upgrade

setup.py

@@ -132,7 +132,7 @@ def extensions():
                       "enum34",
                       "mockextras",
                       "pandas",
-                      "pymongo>=3.0",
+                      "pymongo==3.4.0",
                       "python-dateutil",
                       "pytz",
                       "tzlocal",