loosen pymongo dependency

Author: p

requirements.txt

@@ -2,5 +2,5 @@ ordereddict==1.1
 python-dateutil==2.7
 matplotlib==1.4.3
 numpy==1.14.5
-pymongo==3.6.1
+pymongo>=3.6.1,<4.0.0
 psutil==5.4.2

setup.py

@@ -17,7 +17,7 @@
     # simplify the default install experience, particularly where a build
     # toolchain is required.
     extras_requires = {
-        "all": ['matplotlib==1.4.3', 'numpy==1.14.5', 'pymongo==3.6.1', 'psutil==5.4.2'],
+        "all": ['matplotlib==1.4.3', 'numpy==1.14.5', 'pymongo>=3.6.1,<4.0.0', 'psutil==5.4.2'],
         "mlaunch": ['pymongo==3.6.1', 'psutil==5.4.2'],
         "mlogfilter": [],
         "mloginfo": ['numpy==1.14.5'],