Fix typo in doxygen group

sg- · sg- · commit cba75f467d73 · 2017-04-12T08:56:36.000-05:00
diff --git a/drivers/SPI.h b/drivers/SPI.h
@@ -70,7 +70,7 @@ namespace mbed {
  *
  * }
  * @endcode
- * @ingroup dirvers
+ * @ingroup drivers
  */
 class SPI {
 
