save direct dependency in package.json with relative path

[davidfirst]

Similar to #506 but with direct dependency.
For example, a component is-string depends on is-type. By default, is-type is saved as an NPM package. As such, the package.json of is-string will have a dependency, something like: "@bit/is-type": "0.0.1".
To update is-type, a user needs to run 'bit import is-type'. During the import, we fix the links and point is-type dependency of is-string to newly imported is-type.
However, in case the user wants to publish his package, it won't work. The npm installation of is-string will save is-type as a package and won't point to the imported is-type.
The solution is to update the package.json of 'is-string' and change the is-type entry from a package to a relative path inside the project.