Fix MimeType Case

Even though mimetypes are supposed to be case insensitive, Android
treats them as case sensitive so it is best practice to do it all
in lowercase.

Change-Id: I2ce2ac2df4db4989d8be36479f07d4bab97dc7bf

prebuilt/common/lib/content-types.properties

@@ -1,8 +1,8 @@
 # If you want to support more recognized mimetypes in libcore.net.MimeUtils, add them here
 
 docm=application/vnd.ms-word.document.macroenabled.12
-xlsb=application/vnd.ms-excel.sheet.binary.macroEnabled.12
+xlsb=application/vnd.ms-excel.sheet.binary.macroenabled.12
 xlsm=application/vnd.ms-excel.sheet.macroEnabled.12
-ppsm=application/vnd.ms-powerpoint.slideshow.macroEnabled.12
+ppsm=application/vnd.ms-powerpoint.slideshow.macroenabled.12
 ppsx=application/vnd.openxmlformats-officedocument.presentationml.slideshow
-pptm=application/vnd.ms-powerpoint.presentation.macroEnabled.12
+pptm=application/vnd.ms-powerpoint.presentation.macroenabled.12