Temp workaround for invalid certificate issue on travis-ci
Merge pull request #202 from cdeil/issue-202

Travis-CI failure due to invalid certificate?
Fix exact elliptical overlap issue
Fix a second bug in the elliptical overlap calculation
Merge pull request #198 from cdeil/issue-198

Bug in exact elliptical photometry
Adding test for aperture plot, it only test whether it runs without a problem
Fixing bug in RectangularAnnulus plot
Add check for matplotlib existence
updating travis.xml to allow matplotlib tests pass