REL: declare compatibility with Python 3.7

Add travis tests with Python 3.7.

Author: pavoljuhas

.travis.yml

@@ -9,6 +9,7 @@ env:
   - MYUSEMC=true MYPYTHON_VERSION=3.4
   - MYUSEMC=true MYPYTHON_VERSION=3.5
   - MYUSEMC=true MYPYTHON_VERSION=3.6
+  - MYUSEMC=true MYPYTHON_VERSION=3.7
   - MYUSEMC=false
 
 git:

README.rst

@@ -23,7 +23,7 @@ http://diffpy.github.io/diffpy.utils.
 REQUIREMENTS
 ------------------------------------------------------------------------
 
-The diffpy.utils package requires Python 3.6, 3.5, 3.4 or 2.7 and
+The diffpy.utils package requires Python 3.4 or later or 2.7 and
 the following software:
 
 * ``setuptools``   - tools for installing Python packages

setup.py

@@ -114,6 +114,7 @@ def getversioncfg():
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
         'Topic :: Scientific/Engineering :: Physics',
     ],
 )