Align speech rate on iOS with Android and documentation (#749)
Align speech rate on iOS with Android and documentation (#749)

According to our docs 1.0 is the normal speaking rate. This currently
is true on Android, but on iOS the default rate is 0.5 and 1 is the
maximum rate.

Fix this by multiplying the specified rate with the default rate on iOS.

fbshipit-source-id: 53dfb96

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