Update setting PATH env for Linux build script

[alexbeattie42]

Fixes issue #3928

Brief summary of changes

Check which shell the user is using and attempt to update path if the shell is bash.

Testing I've completed

Ran the build script multiple times to ensure that .bashrc is updated if variable exists and created if it doesn't.

Looking for feedback on...

• Is is suitable to assume the system will have grep, and sed available?

CHANGELOG.md (choose one)

• no need to update because the change only affects a build script

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This change is 

[nickbianco]

@alexbeattie42 sorry for the delay! Giving this a test locally now.