Remove race flag when testing on windows environment

Seems to be related to golang/go#23649.

Author: bpicode

appveyor.yml

@@ -18,4 +18,4 @@ build_script:
   - gcc --version
 
 test_script:
-  - for /f "" %%G in ('go list ./... ^| find /i /v "/vendor/"') do ( go test -race %%G & IF ERRORLEVEL == 1 EXIT 1)
+  - for /f "" %%G in ('go list ./... ^| find /i /v "/vendor/"') do ( go test %%G & IF ERRORLEVEL == 1 EXIT 1)