Change `arrow` pointer to `I`pointer on selecting text

[Paarmita]

Current problem
On selecting any text in the extension, the arrow pointer remains the same and doesn't change.

Expected Behaviour
The arrow icon should change to a pointer or I icon on selecting text, in order to show that text has been selected.

[uimarshall]

Hi April,

I am an outreachy applicant and looking forward to contributing to this project.
I want to find out if I could work on it.

[april]

If you want to fix this, that would be great @Paarmita. Thanks!

[Paarmita]

@april Thanks. I will work on it.

[april]

Fixed in #37.