fix wrong type in mkevent and main

src/main.c

@@ -10,7 +10,7 @@ int main(int argc, char *argv[]) {
 
 	if (argc < 2) {
 		printf("not enough options\n");
-		printf("usage: %c -l -n DATE EVENT_NAME\n", argv[0]);
+		printf("usage: %s -l -n DATE EVENT_NAME\n", argv[0]);
 		return 1;
 	}
 

src/mkevent.c

@@ -18,7 +18,7 @@ char mkevent(int argc, char *argv[]) {
 	} */
 
 	if (argc < 3) {
-		printf("usage: %c [-n] DATE EVENT_NAME\n", argv[0]);
+		printf("usage: %s [-n] DATE EVENT_NAME\n", argv[0]);
 		return 1;
 	}