Update location emsdk_set_env.bat in emsdk.bat (#553)

The location of this file is now fixed to living inside the
emsdk directory, not the current working directory.
diff --git a/emsdk.bat b/emsdk.bat
index 3a95825..0decd1d 100644
--- a/emsdk.bat
+++ b/emsdk.bat
@@ -42,10 +42,10 @@
 

 @set EMSDK_PY=

 

-:: python is not able to set environment variables to the parent calling process, so

-:: therefore have it craft a .bat file, which we invoke after finishing python execution,

-:: to set up the environment variables

-@IF EXIST emsdk_set_env.bat (

-  @CALL emsdk_set_env.bat > NUL

-  @DEL /F /Q emsdk_set_env.bat

+:: python is not able to set environment variables to the parent calling

+:: process, so therefore have it craft a .bat file, which we invoke after

+:: finishing python execution, to set up the environment variables

+@IF EXIST "%~dp0\emsdk_set_env.bat" (

+  @CALL "%~dp0\emsdk_set_env.bat" > NUL

+  @DEL /F /Q "%~dp0\emsdk_set_env.bat"

 )