string-util: fix typo

Follow-up for 63566c6b6f.

src/basic/string-util.c

@@ -1512,14 +1512,14 @@ char *strrstr(const char *haystack, const char *needle) {
         const char *f = NULL;
         size_t l;
 
-        /* Like strstr() but returns the last rather than the first occurence of "needle" in "haystack". */
+        /* Like strstr() but returns the last rather than the first occurrence of "needle" in "haystack". */
 
         if (!haystack || !needle)
                 return NULL;
 
         l = strlen(needle);
 
-        /* Special case: for the empty string we return the very last possible occurence, i.e. *after* the
+        /* Special case: for the empty string we return the very last possible occurrence, i.e. *after* the
          * last char, not before. */
         if (l == 0)
                 return strchr(haystack, 0);