elevate conda-forge channel to highest priority

hopefully this will fix the build on osx which seems to suffer from the
problems described in conda-forge/numpy-feedstock#47

1.0.3_py27/construct.yaml

@@ -2,8 +2,8 @@ name: ObsPy
 version: 1.0.3-py27_3
 
 channels:
-  - http://repo.continuum.io/pkgs/free/
   - https://conda.anaconda.org/conda-forge
+  - http://repo.continuum.io/pkgs/free/
   - https://conda.anaconda.org/obspy
 
 specs: