Add back api= as an attribute to @RequiresApi

I changed the api= attribute to value= to make the
annotation more convenient to use, but apparently that
CL didn't make it into the beta1 build, so now that
code may be referencing api=, we'll need to include it
as well.

Change-Id: I5b267193923e28d4d45631c0715b460083fca828
1 file changed