Fix warning: implicit declaration of function ‘wait’

[devurandom]

Fixes the following compiler warning:

.../src/drip_daemon.c: In function ‘main’:                         
.../src/drip_daemon.c:46:5: warning: implicit declaration of function ‘wait’ [-Wimplicit-function-declaration]                                                
     wait(&status);                                                                        
     ^~~~