MNT: Don't pin matplotlib 1.5 builds to numpy 1.9

Conda doesn't have packages for that combination.

Author: dopplershift

.travis.yml

@@ -13,8 +13,8 @@ env:
     - CONDA_DEPENDENCIES="pytest matplotlib nose coverage"
     - PIP_DEPENDENCIES="pytest-cov coveralls"
   matrix:
-    - PYTHON_VERSION=3.3 MATPLOTLIB_VERSION=1.5 NUMPY_VERSION=1.9
-    - PYTHON_VERSION=3.4 MATPLOTLIB_VERSION=1.5 NUMPY_VERSION=1.9
+    - PYTHON_VERSION=3.3 MATPLOTLIB_VERSION=1.5
+    - PYTHON_VERSION=3.4 MATPLOTLIB_VERSION=1.5
     - PYTHON_VERSION=2.7 MATPLOTLIB_VERSION=1.5
     - PYTHON_VERSION=3.5 MATPLOTLIB_VERSION=1.5
     - PYTHON_VERSION=2.7 MATPLOTLIB_VERSION=2.0