MDL-48620 JavaScript: Update .jshintrc to comply with coding style

* eqeqeq: We do not require use of ===
* maxlen: Coding style aims for 132 characters
* indent: 4 Characters (Helps some editors but does not warn in new version of jshint)
* undef: Warn about variables used before they are defined
* predef: Specify that we define the M variable elsewhere