BLD: update 2.7 build (doc build) to use matplotlib 1.3.1

Author: jreback

ci/requirements-2.7.txt

@@ -6,7 +6,7 @@ cython==0.19.1
 bottleneck==0.6.0
 numexpr==2.2.2
 tables==2.3.1
-matplotlib==1.1.1
+matplotlib==1.3.1
 openpyxl==1.6.2
 xlsxwriter==0.4.6
 xlrd==0.9.2