Fix powershell file association after emsdk script rename (#340)

See #292

Fixes #336

emsdk.ps1

@@ -26,7 +26,7 @@ if (-Not $EMSDK_PY) {
 # Tell EMSDK to create environment variable setter as a .ps1 file
 $env:EMSDK_POWERSHELL = 1
 
-& $EMSDK_PY "$ScriptDirectory/emsdk" $args
+& $EMSDK_PY "$ScriptDirectory/emsdk.py" $args
 
 # python is not able to set environment variables to the parent calling process, so
 # therefore have it craft a .ps1 file, which we invoke after finishing python execution,