Fix the .PHONY declaration

Author: rexim

Makefile

@@ -1,7 +1,7 @@
 build/counter: examples/counter.c coroutine.h build/coroutine.a
 	gcc -I. -Wall -Wextra -ggdb -o build/counter examples/counter.c build/coroutine.a
 
-.PHONY:
+.PHONY: examples
 examples: build/counter build/counter_cpp build/counter_c3 build/counter_jai build/echo
 
 build/echo: examples/echo.c3 coroutine.c3 build/coroutine.a