get_cached_default_environment: cache by VIRTUAL_ENV only

[blueyed]

Fixes #1200

[codecov-io]

Codecov Report

Merging #1201 into master will decrease coverage by 0.23%.
The diff coverage is 87.5%.

@@            Coverage Diff             @@
##           master    #1201      +/-   ##
==========================================
- Coverage   92.86%   92.62%   -0.24%     
==========================================
  Files          57       57              
  Lines        6910     6916       +6     
==========================================
- Hits         6417     6406      -11     
- Misses        493      510      +17

Impacted Files	Coverage Δ
jedi/api/environment.py	81.72% <87.5%> (+0.05%)	⬆️
jedi/cache.py	71.23% <0%> (-21.92%)	⬇️

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[davidhalter]

What I meant to say in #1200 was this:

def get_cached_default_environment():
    environment = _get_cached_default_environment()
    if environment.prefix != <virtualenv_variable>:
        _get_cached_default_environment.reset()
        return _get_cached_default_environment()
    return environment

# Rename 
@time_cache(seconds=10 * 60)
def _get_cached_default_environment():
    return get_default_environment()

Obviously you would also need to add the reset function for time_cache. It doesn't exist, yet.

[davidhalter]

I changed it now in a bit of a different way, but thanks still for your initial thoughts!