Version grass 8 0 0alpha (#1620)

Set preview release version

* GRASS GIS 8.0.0alpha
* g.extension: Windows version workaround

include/VERSION

@@ -1,4 +1,4 @@
 8
 0
-dev
+0alpha
 2021

scripts/g.extension/g.extension.py

@@ -1288,7 +1288,8 @@ def install_extension_win(name):
             "platform": platform,
             "major": version[0],
             "minor": version[1],
-            "patch": version[2],
+            # "patch": version[2],
+            "patch": "dev",
         }
     )