Rename suitableForHeavilyDisabled to suitableForSeverelyDisabled

"heavily disabled" is not a correct term to describe a person with severe disabilities, all major dictionaries use "severely disabled" instead.

OJP/OJP_Trips.xsd

@@ -1222,7 +1222,7 @@ Can only be used when both participants recognise the same schedule version. If
 			<xs:enumeration value="automaticRamp"/>
 			<xs:enumeration value="suitableForWheelchairs"/>
 			<xs:enumeration value="suitableForUnassistedWheelchairs"/>
-			<xs:enumeration value="suitableForHeavilyDisabled"/>
+			<xs:enumeration value="suitableForSeverelyDisabled"/>
 			<xs:enumeration value="suitableForPushchairs"/>
 			<xs:enumeration value="suitableForBicycles"/>
 			<xs:enumeration value="tactilePlatformEdges"/>