vpxenc: change --framerate to --fps

Saves a little typing. FPS is a well known abbreviation.

Change-Id: I53730ea36afb9309732eb1c72c52d824d5365fec

vpxenc.c

@@ -766,7 +766,7 @@ static const arg_def_t verbosearg       = ARG_DEF("v", "verbose", 0,
         "Show encoder parameters");
 static const arg_def_t psnrarg          = ARG_DEF(NULL, "psnr", 0,
         "Show PSNR in status line");
-static const arg_def_t framerate        = ARG_DEF(NULL, "framerate", 1,
+static const arg_def_t framerate        = ARG_DEF(NULL, "fps", 1,
         "Stream frame rate (rate/scale)");
 static const arg_def_t use_ivf          = ARG_DEF(NULL, "ivf", 0,
         "Output IVF (default is WebM)");