Fix tab bar indicator

[FedeBossman]

Description

Tab bar indicator would not animate as expected. This PR lets devs change the selected tab from the input.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes, dev for new features, new releases and breaking changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)
• I've added new examples (applies to new features and breaking changes in core library)

[alexzoul]

It was fixed on #161