Update MaterialDatePicker.java

there was a simple bug on setDatePickerValue. the variable "value" was printed as a string.

Author: centamiv

src/main/java/gwt/material/design/client/ui/MaterialDatePicker.java

@@ -53,7 +53,7 @@ public static native String getDatePickerValue(String id)/*-{
 	}-*/;
 
 	private static native void setDatePickerValue(String value)/*-{
-		$wnd.jQuery('.datepicker').val("value");
+		$wnd.jQuery('.datepicker').val(value);
 	}-*/;
 
 	public static native void initDatePicker()/*-{