Fix typos in code comments

sample/src/main/java/com/kunzisoft/switchdatetimesample/Sample.java

@@ -90,7 +90,7 @@ public void onNegativeButtonClick(Date date) {
 
             @Override
             public void onNeutralButtonClick(Date date) {
-                // Optional if neutral button does'nt exists
+                // Optional if neutral button doesn't exist
                 textView.setText("");
             }
         });

switchdatetime/src/main/java/com/kunzisoft/switchdatetime/date/widget/ListPickerYearView.java

@@ -16,7 +16,7 @@
 import java.util.ArrayList;
 
 /**
- * ListView for select one year, year selected is highlight <br />
+ * ListView to select one year, year selected is highlighted <br />
  * To get the year, assign an OnYearSelectedListener
  * @see com.kunzisoft.switchdatetime.date.OnYearSelectedListener#onYearSelected(View, int)
  * @author JJamet

switchdatetime/src/main/java/com/kunzisoft/switchdatetime/date/widget/YearPickerAdapter.java

@@ -15,7 +15,7 @@
 import java.util.Locale;
 
 /**
- * Adapter for manage elements of ListPickerYearView
+ * Adapter for managing elements of ListPickerYearView
  * @author JJamet
  */
 class YearPickerAdapter extends RecyclerView.Adapter<YearPickerAdapter.TextIndicatorViewHolder> {