Fix typo in class Button docs
* (i.e. when the button changes from not pressed to pressed, and vice versa).
* However, if the button is pressed and held longer than repeat_start_interval
* milliseconds, the press will be emitted once again, and then again every
- * repeat_interval milliseconds untill the press is released. To
+ * repeat_interval milliseconds until the press is released. To
* disable this feature, set repeat_start_interval to -1.
*/
class Button : public DigitalInput, public BooleanProducer {
