Added animation to subscribe icon

[samagragupta]

Fixes #57

Checklist

• [x] I have read the Contribution & Best practices Guide and my PR follows them.
• [x] My branch is up-to-date with the Upstream branch.
• [x] I have added necessary documentation (if appropriate)

Changes proposed in this pull request:

Added animation to subscribe icon when the mouse has hovered on the subscribe button.

Screenshots for the change

[samagragupta]

@0x48piraj @mariobehling Please review.