Fixed bug where method ew returned int but reducer magneticVariation expected float. This allowed since int is assignable to float.

    @Terminal(expression = "[WE]")
    protected int ew(char c)
    {
        return 'E' == c ? 1 : -1;
    }

    @Rule("decimal c ew")
    protected void magneticVariation(
            float magneticVariation, // degrees
            float mew,
            @ParserContext("data") NMEAObserver data)
    {
        data.setMagneticVariation(mew * magneticVariation);
    }