fix non-ASCII character (microsoft#2894)

It causes C4819 again. It should be fixed in ArduPilot/pymavlink#438

MavLinkCom/mavlink/mavlink_types.h

@@ -68,7 +68,7 @@ typedef struct param_union {
  * The intention is that by replacing the is_double bit with 0 the type can be directly used as a double (as the is_double bit corresponds to the
  * lowest mantissa bit of a double). If is_double is 0 then mavlink_type gives the type in the union.
  * The mavlink_types.h header will also need to have shifts/masks to define the bit boundaries in the above,
- * as bitfield ordering isn’t consistent between platforms. The above is intended to be for gcc on x86,
+ * as bitfield ordering isn't consistent between platforms. The above is intended to be for gcc on x86,
  * which should be the same as gcc on little-endian arm. When using shifts/masks the value will be treated as a 64 bit unsigned number,
  * and the bits pulled out using the shifts/masks.
 */