mark full import statement instead of path node

[benmosher]

for things like no-unresolved, mark the full import when there is a problem with the path, since

• it looks bad right now in Sublime, at least (only highlights opening quote)
• semantically, if the path is not usable the whole import is botched anyway

[ljharb]

Hmm, wouldn't it make more sense to mark the entire path string, as opposed to the import statement?

In other words, the "mark" is usually where i put my cursor to fix the problem; so i'd expect it to be at the specifier.