docs: fix simple typo, migitate -> mitigate

There is a small typo in src/sp_utils.c.

Should read `mitigate` rather than `migitate`.

src/sp_utils.c

@@ -127,7 +127,7 @@ static int construct_filename(char* filename,
   }
 
   /* We're using the sha256 sum of the rule's textual representation
-   * as filename, in order to only have one dump per rule, to migitate
+   * as filename, in order to only have one dump per rule, to mitigate
    * DoS attacks. */
   PHP_SHA256Init(&context);
   PHP_SHA256Update(&context, (const unsigned char*)ZSTR_VAL(textual),