typo fix, thx to gemal

extensions/xforms/resources/locale/en-US/xforms.properties

@@ -4,7 +4,7 @@ schemaLoadError      = XForms Error (3): Failed to load schema
 instanceLoadError    = XForms Error (4): Failed to load instance
 mipParseError        = XForms Error (5): Error while parsing model item property: %S
 nodesetEvaluateError = XForms Error (6): Error evaluating nodeset expression: %S
-multiMIPError        = XForms Error (7): Multiply defined model item property on element
+multiMIPError        = XForms Error (7): Multiple defined model item property on element
 idRefError           = XForms Error (8): id (%S) does not refer to a %S element
 indexEvalError       = XForms Error (9): Error evaluating index attribute: %S
 exprParseError       = XForms Error (10): Error parsing XPath expression: %S