Update lombscargle.py

[hamzaallen]

Define two functions that calculate the rms and rms error of the spectrum over a specific range of frequencies.

Relevant Issue(s)/PR(s)

Provide an overview of the implemented solution or the fix and elaborate on the modifications.

Is there a new dependency introduced by your contribution? If so, please specify.

Any other comments?

[pep8speaks]

Hello @hamzaallen! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file stingray/lombscargle.py:

Line 390:1: W293 blank line contains whitespace Line 394:1: W293 blank line contains whitespace Line 395:1: W293 blank line contains whitespace Line 396:1: W293 blank line contains whitespace Line 397:5: E303 too many blank lines (4) Line 400:1: W293 blank line contains whitespace Line 401:9: E303 too many blank lines (3) Line 430:1: W293 blank line contains whitespace Line 431:1: W293 blank line contains whitespace Line 432:5: E303 too many blank lines (2) Line 470:1: W293 blank line contains whitespace