Fix syntax for "[" command

[wtanaka]

== is a bash-ism

dash:

$ if [ "a" == "b" ]; then echo true; else echo false; fi
dash: 1: [: a: unexpected operator
false
$ if [ "a" == "a" ]; then echo true; else echo false; fi
dash: 2: [: a: unexpected operator
false
$ if [ "a" = "b" ]; then echo true; else echo false; fi
false
$ if [ "a" = "a" ]; then echo true; else echo false; fi
true

bash:

$ if [ "a" == "b" ]; then echo true; else echo false; fi
false
$ if [ "a" == "a" ]; then echo true; else echo false; fi
true
$ if [ "a" = "b" ]; then echo true; else echo false; fi
false
$ if [ "a" = "a" ]; then echo true; else echo false; fi
true

zsh:

% if [ "a" == "b" ]; then echo true; else echo false; fi
zsh: = not found
% if [ "a" == "a" ]; then echo true; else echo false; fi
zsh: = not found
% if [ "a" = "b" ]; then echo true; else echo false; fi
false
% if [ "a" = "a" ]; then echo true; else echo false; fi
true

[wtanaka]

@neillturner thanks for #23 (comment) !

I still think the shell syntax is incorrect though -- I pasted some small test cases to this pull request description to illustrate.

[neillturner]

ok. i mostly consider bash. but i will test this and as long as it works merge and release