tool_main: fix typo in comment

The referred to library is NSPR, so fix the switched around characters.

src/tool_main.c

@@ -214,7 +214,7 @@ static void main_free(struct GlobalConfig *config)
   convert_cleanup();
 #ifdef USE_NSS
   if(PR_Initialized()) {
-    /* prevent valgrind from reporting still reachable mem from NSRP arenas */
+    /* prevent valgrind from reporting still reachable mem from NSPR arenas */
     PL_ArenaFinish();
     /* prevent valgrind from reporting possibly lost memory (fd cache, ...) */
     PR_Cleanup();