avfilter: bump version for the latest API change

And fix the entry in doc/APIchanges
Signed-off-by: James Almer <jamrial@gmail.com>

doc/APIchanges

@@ -15,7 +15,7 @@ libavutil:     2017-10-21
 
 API changes, most recent first:
 
-2018-xx-xx - xxxxxxx - lavc 7.13.100 - avcodec.h
+2018-xx-xx - xxxxxxx - lavfi 7.14.100 - avfilter.h
   Deprecate use of avfilter_register(), avfilter_register_all(),
   avfilter_next(). Add av_filter_iterate().
 

libavfilter/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   7
-#define LIBAVFILTER_VERSION_MINOR  13
+#define LIBAVFILTER_VERSION_MINOR  14
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \