Update linkedin.py

[omarDans]

I updated the init method of the Linkeding class

First of all, in the line 19 was an error because you forgot '()' so the comparison wasnt working at all:
if (platform.system == "Linux"):

Also, following the flow of the program, i think the previous check doesnt make anysense at all so i moved it to the else statement from the if at line 17:
if (len(linkedinEmail)>0):

Now if the user provided the gmail and password is going to try to authenticate that way, if the user didnt provide the credentials, it's going to correctly check if the script's is being executed from linux and then if the 'firefoxProfileRootDir' variable is defined, if it is not, it will through error and exit.

[aminblm]

Thank you @omarDans for your PR, I will review it and merge if all goes well.

Surely I left some unchecked errors for now but I will resume work on this sooner than later.