Fix a typo.

src/t_string.c

@@ -316,7 +316,7 @@ void msetGenericCommand(client *c, int nx) {
     }
 
     /* Handle the NX flag. The MSETNX semantic is to return zero and don't
-     * set anything if at least one key alerady exists. */
+     * set anything if at least one key already exists. */
     if (nx) {
         for (j = 1; j < c->argc; j += 2) {
             if (lookupKeyWrite(c->db,c->argv[j]) != NULL) {