Constant definition error
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repository's issues are reserved for feature requests and bug reports.

* **I'm submitting a ...**
  - [x] bug report
  - [ ] feature request
  - [ ] support request => Please do not submit support request here, see note
  at the top of this template.


* **What is the current behavior?**
importing nimgl throws this during compilation:
```bash
C:\...\.nimble\pkgs\nimgl-0.3.6\nimgl\opengl.nim(69, 39) Error: -1 can't be converted to uint64
```


* **If the current behavior is a bug, please provide the steps to reproduce and
if possible a minimal demo of the problem**
Just importing `nimgl` creates the error



* **Please tell us about your environment:**
  
  - Version: [ nimgl 0.3.6 | Nim 1.0.99 [Windows: amd64] ]
  - OS: [ Windows ]
  - Bindings: [ GLFW ]
  - Backend: [ C ]

