Added shield power-up

[AayushiJapsare15]

What does this PR do?

fixes #86

Shield power up is now added which will provide protection from aliens for 3 secs.

Fixes #86

Type of change

• Chore (refactoring code, technical debt, workflow improvements)
• New feature (non-breaking change which adds functionality)

How should this be tested?

• start the game.

Mandatory Tasks

• Make sure you have self-reviewed the code. A decent size PR without self-review might be rejected.

@YadavAkhileshh please merge the PR

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[AayushiJapsare15]

@YadavAkhileshh Please add hacktoberfest-accpeted label, as it is not accepting this PR and others as well.

[YadavAkhileshh]

@AayushiJapsare15 please solve the merge conflict and then try to raise pr