fix(command): prevent failing execvp to return

src/command.c

@@ -1,5 +1,7 @@
 #include "command.h"
 
+#include <errno.h>
+#include <stdlib.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
@@ -7,7 +9,7 @@ unsigned char invoke(struct Args args) {
   pid_t child = fork();
   if (child == 0) {
     execvp(args.argv[0], args.argv);
-    return 1;
+    exit(errno);
   }
   waitpid(child, NULL, 0);