Import failed on Anaconda 3 on Mac OS Catalina 10.15.4
Here is the error I have when I just try to import pyxel.

```
> python /Users/login/test.py
Traceback (most recent call last):
  File "/Users/login/test.py", line 3, in <module>
    import pyxel
  File "//Users/login/anaconda3/lib/python3.7/site-packages/pyxel/__init__.py", line 10, in <module>
    from . import core  # type: ignore
  File "//Users/login/anaconda3/lib/python3.7/site-packages/pyxel/core/__init__.py", line 43, in <module>
    _lib = _load_library()
  File "//Users/login/anaconda3/lib/python3.7/site-packages/pyxel/core/__init__.py", line 40, in _load_library
    return cdll.LoadLibrary(lib_path)
  File "//Users/login/anaconda3/lib/python3.7/ctypes/__init__.py", line 442, in LoadLibrary
    return self._dlltype(name)
  File "//Users/login/anaconda3/lib/python3.7/ctypes/__init__.py", line 364, in __init__
    self._handle = _dlopen(self._name, mode)
OSError: dlopen(//Users/login/anaconda3/lib/python3.7/site-packages/pyxel/core/bin/macos/libpyxelcore.dylib, 6): Library not loaded: /usr/local/opt/sdl2_image/lib/libSDL2_image-2.0.0.dylib
  Referenced from: //Users/login/anaconda3/lib/python3.7/site-packages/pyxel/core/bin/macos/libpyxelcore.dylib
  Reason: image not found
```