Improve clarity of ESLint failure reports

[andrewnicols]

As suggested by Brendan, I've added two things here:

• An INFO line to indicate that ESLint reported JS errors
• A copy of the offending with a caret pointing to the exact failure

I have also taken out the source from the brackets to make the line length shorter.
If there is no column, then the whole line is printed without any caret underneath.

Before:

➜  73808 git:(MDL-75365-master) ✗ php local/ci/mustache_lint/mustache_lint.php -f=`pwd`/lib/templates/welcome.mustache --basename=`pwd` -v=https://html5.validator.nu
/Users/nicols/Sites/public_html/73808/lib/templates/welcome.mustache - WARNING: ESLint error []: Parsing error: Unexpected token foo ( let foo = 'bar'; ), Line: 2 Column: 5

After:

➜  73808 git:(MDL-75365-master) ✗ php local/ci/mustache_lint/mustache_lint.php -f=`pwd`/lib/templates/welcome.mustache --basename=`pwd` -v=https://html5.validator.nu
/Users/nicols/Sites/public_html/73808/lib/templates/welcome.mustache - INFO: ESLint reported JavaScript errors
/Users/nicols/Sites/public_html/73808/lib/templates/welcome.mustache - WARNING: ESLint error []: Parsing error: Unexpected token foo, Line: 2 Column: 5
/Users/nicols/Sites/public_html/73808/lib/templates/welcome.mustache - WARNING: let foo = 'bar';
/Users/nicols/Sites/public_html/73808/lib/templates/welcome.mustache - WARNING:     ^

[brendanheywood]

🥳

[stronk7]

Oh, just came here after looking to #251 . Is this an alternative to it?

In any case, it seems that some tests need to be amended to fulfil the new expected output (and also, to rebase this on top of current master).

Ciao :-)

[andrewnicols]

Oh, just came here after looking to #251 . Is this an alternative to it?

No, this change follows from that one and is based on it.
The other change is obvious and requires little discussion, whilst this one is more contentious so I split tem.

In any case, it seems that some tests need to be amended to fulfil the new expected output (and also, to rebase this on top of current master).

I amended existing tests which should cover this.