make width and height accept string or number

[natepappenhagen]

Currently, height and width are have PropTypes that limit the values to be only numbers.

But, the <svg/> tag doesn't have such a limitation, making valid height/width arguments like this

    <USAMap
      customize={stateConfigurations}
      defaultFill="#F8F8F8"
      height={'100%'}
      width={'100%'}
    />

Very noisy in the console.

[natepappenhagen]

@gabidavila