Fix wrong calculation of width and height after device rotation

[kostyaVyrodov]

Is it a bugfix?

• Yes
• Issue (fix Landscape mode #36)

Describe what you've done:

• I moved code that gets width and height to the initState() function

Steps to reproduce the issue (iOS):

Precondition:
<Swiper index={this.state.selectedPageIndex} onIndexChanged={(index) => this.setState({ selectedPageIndex: index })}> <SomeView/> </Swiper>

• Add function to handle onIndexChanged
• Pass updatedIndex

Steps:

• Rotate device
• Swipe

[arribbar]

Thanks @kostyaVyrodov