compile error after enable install! 'cocoapods', generate_multiple_pod_projects: true in Podfile

### Context and Description

### Environment Details

* coobjc version:1.2.0
* iOS version:12
* Xcode version:10.2.1
* Other informations:

### Expected behavior

### Actual behavior

import cocore header error in coobjc

### Steps to Reproduce

### method call stacks

Start by reproducing the import cocore header error with coobjc 1.2.0 on iOS 12 and Xcode 10.2.1, using the Podfile setting generate_multiple_pod_projects: true. Check the generated pod projects and header paths; done means the installed project compiles without the import error.

Written by the indexing model from the issue text.