Changed compile time check to a runtime check, so that the contentInset is only set on iOS7+.
Changed compile time check to a runtime check, so that the contentInset is only set on iOS7+.

Signed-off-by: Denis Zamataev <a7324680ba0b931ee70e3fe8af95b5d8add0b3bd@gmail.com>

orta/TSMiniWebBrowser,DZamataev/DZTSMiniWebBrowser,alloy/TSMiniWebBrowser,dblock/TSMiniWebBrowser