Clarify differentiate() coordinate values.
Switch to miniconda test environment.
Update image results for later freetype.
Move cfchecker into conda env
Merge pull request #1262 from rhattersley/miniconda

Switch Travis environment to miniconda.
Bump version to 1.7.1
Bump version to 1.7.2-DEV
Add skip_data for tests that require it.
Merge pull request #1263 from QuLogic/tests-skip_data

Add skip_data for tests that require it.
Merge pull request #1253 from rhattersley/differentiate-docs

Clarify differentiate() coordinate values.
fixed tolerance bug in intersection
review actions
Explicitly set version of gribapi
BUG: Fixed varname setting in aux con.
Merge pull request #1283 from cpelley/corrected_netcdf_varname

BUG: Fixed varname setting in aux con.
Merge pull request #1282 from dkillick/explicit_gribapi_ver

Explicitly set version of gribapi in .travis.yml
Merge pull request #1271 from esc24/intersectionbug17

Fixed tolerance bug in intersection
Pin matplotlib to v1.3.1 to preserve test results.
Merge pull request #1293 from rhattersley/pin-matplotlib

Pin matplotlib to v1.3.1 to preserve test results.
BUG: Do not filter surface altitude/pressure fields