[appveyor] activate conda

appveyor.yml

@@ -37,6 +37,7 @@ install:
   - if [%COMPILER%]==[clang-cl] conda install --yes clangdev ninja cmake
   - if [%COMPILER%]==[clang-cl] call "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" amd64
   
+  - if [%COMPILER%]==[flang] call C:\Miniconda36-x64\Scripts\activate.bat
   - if [%COMPILER%]==[flang] conda config --add channels conda-forge isuruf/label/flang --force
   - if [%COMPILER%]==[flang] conda install --yes clangdev flangdev cmake
   - if [%COMPILER%]==[flang] call "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" amd64