Fix typo that prevents Velociraptor showing up in time pie chart

Time spent in Velociraptor doesn't show in the pie chart from analyse_runtime.py in the current master because the word 'invocation' is spelled differently between swift's stdout and the string the script looks for. This (single character) pull request corrects the spelling in swift.

src/velociraptor_interface.c

@@ -745,7 +745,7 @@ void velociraptor_invoke(struct engine *e, const int linked_with_snap) {
 
   /* Report timing */
   if (e->verbose)
-    message("VR Invokation of velociraptor took %.3f %s.",
+    message("VR Invocation of velociraptor took %.3f %s.",
             clocks_from_ticks(getticks() - tic), clocks_getunit());
 
   tic = getticks();