In Small Devices there is overflow issue in Login and Register screen.

[Sagar Zala]

Login Error:

════════ Exception caught by rendering library ═════════════════════════════════════════════════════
The following assertion was thrown during layout:
A RenderFlex overflowed by 26 pixels on the bottom.

The relevant error-causing widget was: 
  Column file:///Users/apple/Downloads/uberr-ui-master/lib/screens/login.dart:50:22
The overflowing RenderFlex has an orientation of Axis.vertical.
The edge of the RenderFlex that is overflowing has been marked in the rendering with a yellow and black striped pattern. This is usually caused by the contents being too big for the RenderFlex.

Consider applying a flex factor (e.g. using an Expanded widget) to force the children of the RenderFlex to fit within the available space instead of being sized to their natural size.
This is considered an error condition because it indicates that there is content that cannot be seen. If the content is legitimately bigger than the available space, consider clipping it with a ClipRect widget before putting it in the flex, or using a scrollable container rather than a Flex, like a ListView.

The specific RenderFlex in question is: RenderFlex#0031b relayoutBoundary=up3 OVERFLOWING
...  needs compositing
...  parentData: offset=Offset(0.0, 0.0); flex=1; fit=FlexFit.tight (can use size)
...  constraints: BoxConstraints(0.0<=w<=330.0, h=353.0)
...  size: Size(330.0, 353.0)
...  direction: vertical
...  mainAxisAlignment: start
...  mainAxisSize: max
...  crossAxisAlignment: start
...  textDirection: ltr
...  verticalDirection: down
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Sign Up Error:

════════ (2) Exception caught by rendering library ═════════════════════════════════════════════════
A RenderFlex overflowed by 100 pixels on the bottom.
The relevant error-causing widget was: 
  Column file:///Users/apple/Downloads/uberr-ui-master/lib/screens/register.dart:52:24
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[Olayemii Garuba]

This PR #29 should fix this issue, you can pull again from the master branch and check if that works.