Change build command for appveyor

This is due to an error that was occurring with scipy. The solution is
to use a conda environment as described in
http://tjelvarolsson.com/blog/how-to-continuously-test-your-python-code-on-windows-using-appveyor/

Author: drvinceknight

appveyor.yml

@@ -1,11 +1,18 @@
 environment:
   matrix:
-    - PYTHON: "C:\\Python35"
-    - PYTHON: "C:\\Python36"
+    - PYTHON_VERSION: "3.5"
+      MINICONDA: "C:\\Miniconda35"
+    - PYTHON_VERSION: "3.6"
+      MINICONDA: "C:\\Miniconda36"
 install:
-  - "%PYTHON%\\python.exe -m pip install -r requirements.txt"
+  - "set PATH=%MINICONDA%;%MINICONDA%\\Scripts;%PATH%"
+  - "conda config --set always_yes yes --set changeps1 no"
+  - "conda update -q conda"
+  - "conda create -q -n test-environment python=%PYTHON_VERSION% scipy>=0.19.0 numpy>=1.9.2"
+  - "activate test-environment"
+  - "python -m pip install -r requirements.txt"
 build: off
 test_script:
-  - "%PYTHON%\\python.exe -m unittest discover"
-  - "%PYTHON%\\python.exe doctests.py"
-  - "%PYTHON%\\python.exe setup.py install"
+  - "python -m unittest discover"
+  - "python doctests.py"
+  - "python setup.py install"