Update .travis.yml

using requirements-windows.txt (windows build)

.travis.yml

@@ -98,7 +98,7 @@ install:
       wget -q https://github.com/lexelby/inkstitch-build-objects/releases/download/v1.0.0/Shapely-1.6.3-cp27-cp27m-win32.whl
       wine c:\\Python\\python.exe c:\\Python\\scripts\\pip.exe install Shapely-1.6.3-cp27-cp27m-win32.whl
 
-      wine c:\\Python\\python.exe c:\\Python\\scripts\\pip.exe install -r requirements.txt
+      wine c:\\Python\\python.exe c:\\Python\\scripts\\pip.exe install -r requirements-windows.txt
 
       set +x
     elif [ "$BUILD" = "osx" ]; then