Update MPNotificationView.podspec

maybe i thinks it cause by "s.platform     = :ios, '4.0'" in podspec

- (void) dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

MPNotificationView.m:44:1: Method possibly missing a [super dealloc] call

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@implementation MPNotificationView

- (void) dealloc
{
    _delegate = nil;
    [self removeGestureRecognizer:_tapGestureRecognizer];
}

MPNotificationView.m:191:1: Method possibly missing a [super dealloc] call

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