The report printed to the console for invalid source map samples has
been improved in a few ways:
* The entire message is now printed using `console.error`, so the
contents aren't split between STDERR and STDOUT
* The code fence is now guaranteed to be a set length, rather than it
varying depending on the filename
* The code fence is no longer padded on the inside with newlines, which
results in a more compact output that is (in my opinion) just as
readable.
