Let ParseFacebook accept expiresIn parameter

[cbaker6]

• Switch the expirationDate to expiresIn and allow it to accept an Int value instead of a Date.
• Fixed bug that prevented limited login from working.
• Let expiresIn be optional since developers using the Facebook SDK won't need it. The optional parameter may be needed for Swift Linux, Android, etc. who don't have a Facebook SDK.

[codecov]

Codecov Report

Merging #104 (4b28303) into main (a233682) will increase coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 4b28303 differs from pull request most recent head b989915. Consider uploading reports for the commit b989915 to get more accurate results

@@            Coverage Diff             @@
##             main     #104      +/-   ##
==========================================
+ Coverage   81.01%   81.02%   +0.01%     
==========================================
  Files          65       65              
  Lines        5474     5477       +3     
==========================================
+ Hits         4435     4438       +3     
  Misses       1039     1039              

Impacted Files	Coverage Δ
...Swift/Authentication/3rd Party/ParseFacebook.swift	100.00% <100.00%> (ø)

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