CI: Update Appveyor root miniconda

xref conda/conda#6251

Closes pandas-dev#18073

Author: TomAugspurger

appveyor.yml

@@ -18,13 +18,13 @@ environment:
 
   matrix:
 
-    - CONDA_ROOT: "C:\\Miniconda3_64"
+    - CONDA_ROOT: "C:\\Miniconda36_64"
       PYTHON_VERSION: "3.6"
       PYTHON_ARCH: "64"
       CONDA_PY: "36"
       CONDA_NPY: "112"
 
-    - CONDA_ROOT: "C:\\Miniconda3_64"
+    - CONDA_ROOT: "C:\\Miniconda36_64"
       PYTHON_VERSION: "2.7"
       PYTHON_ARCH: "64"
       CONDA_PY: "27"