Fix version in AppVeyor config (GH-5124)

diff --git a/.github/appveyor.yml b/.github/appveyor.yml
index b7a0133..b7d4078 100644
--- a/.github/appveyor.yml
+++ b/.github/appveyor.yml
@@ -1,4 +1,4 @@
-version: 3.7.0a0.{build}
+version: 3.7build{build}
 clone_depth: 5
 branches:
   only: