suppress warning about asprintf

[dradetsky]

otherwise you get the following from make:

keynav.c: In function ‘addbinding’:
keynav.c:376:9: warning: implicit declaration of function ‘asprintf’; did you mean ‘vsprintf’? [-Wimplicit-function-declaration]
         asprintf(&newrecordingpath, "%s/%s", getenv("HOME"), path + 2);
         ^~~~~~~~
         vsprintf