Bump ABI version

Due to recent changes to command line options for rate control
parameters.

Change-Id: I1de7cb4ff2850a3ed19ec216dd9d07f64a118e92

vpx/vpx_encoder.h

diff --git a/vpx/vpx_encoder.h b/vpx/vpx_encoder.h
index c4589be..f8fdfc0 100644
--- a/vpx/vpx_encoder.h
+++ b/vpx/vpx_encoder.h
@@ -58,7 +58,7 @@
  * fields to structures
  */
 #define VPX_ENCODER_ABI_VERSION \
-  (14 + VPX_CODEC_ABI_VERSION + \
+  (15 + VPX_CODEC_ABI_VERSION + \
    VPX_EXT_RATECTRL_ABI_VERSION) /**<\hideinitializer*/
 
 /*! \brief Encoder capabilities bitfield