fix index name clash for multiple models.

[rselk]

No description provided.

[rselk]

fixes #128

[mceachen]

 NoMethodError:
   undefined method `migration_template' for #<ClosureTree::Generators::MigrationGenerator:0x00000004470c58>

[seuros]

Weird, error. Tests pass locally.
@mceachen do you have an idea about this error ?

[mceachen]

I've never used that gem before, so we'll have to see what it's trying to
do.

Odd that they pass locally though.

[seuros]

[mceachen]

I found out that if the generator tests run in a separate process from the other tests, everything is fine.

I created yet another spec group just for your new spec, and https://travis-ci.org/mceachen/closure_tree/builds/39798412 just passed, so finger's crossed...