update documentation string in pexpect/__init__.py to be compatible with python 2 and 3
update documentation string in pexpect/__init__.py to be compatible with python 2 and 3

bangi123/pexpect,dongguangming/pexpect,crdoconnor/pexpect,dongguangming/pexpect,bangi123/pexpect,Wakeupbuddy/pexpect,Depado/pexpect,nodish/pexpect,blink1073/pexpect,Depado/pexpect,nodish/pexpect,bangi123/pexpect,Depado/pexpect,dongguangming/pexpect,Wakeupbuddy/pexpect,crdoconnor/pexpect,dongguangming/pexpect,blink1073/pexpect,bangi123/pexpect,Wakeupbuddy/pexpect,crdoconnor/pexpect,quatanium/pexpect,blink1073/pexpect,Depado/pexpect,quatanium/pexpect,Wakeupbuddy/pexpect,nodish/pexpect,quatanium/pexpect