Correct typo in GRADLE_OPTS for Windows

The -XX:MaxHeapSize option should include the 'm' postfix to signify
that the value is megabytes rather than bytes.

gradlew.bat

@@ -9,7 +9,7 @@
 if "%OS%"=="Windows_NT" setlocal
 
 @rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
-set GRADLE_OPTS=-XX:MaxPermSize=1024m -Xmx1024m -XX:MaxHeapSize=256 %GRADLE_OPTS%
+set GRADLE_OPTS=-XX:MaxPermSize=1024m -Xmx1024m -XX:MaxHeapSize=256m %GRADLE_OPTS%
 set DEFAULT_JVM_OPTS=
 
 set DIRNAME=%~dp0