Fix typo

Author: Thomas Munro

Author: mhagander

src/include/storage/dsm_impl.h

@@ -72,7 +72,7 @@ extern bool dsm_impl_op(dsm_op op, dsm_handle handle, Size request_size,
 /* Some implementations cannot resize segments.  Can this one? */
 extern bool dsm_impl_can_resize(void);
 
-/* Implementation-dependent actions required to keep segment until shudown. */
+/* Implementation-dependent actions required to keep segment until shutdown. */
 extern void dsm_impl_pin_segment(dsm_handle handle, void *impl_private);
 
 #endif   /* DSM_IMPL_H */