Fix using .lstrip() in hivemind.compression

[borzunov]

.lstrip() doesn't do what I though it does. In fact, it would remove any prefixes with chars {'t', 'o', 'r', 'c', 'h', '.'}, which is not what we expect (even though it works here).

[codecov]

Codecov Report

Merging #578 (4a07742) into master (ec1d7fe) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #578      +/-   ##
==========================================
- Coverage   85.37%   85.33%   -0.04%     
==========================================
  Files          81       81              
  Lines        8006     8006              
==========================================
- Hits         6835     6832       -3     
- Misses       1171     1174       +3     

Impacted Files	Coverage Δ
hivemind/compression/base.py	94.28% <100.00%> (ø)
hivemind/compression/quantization.py	94.82% <100.00%> (ø)

... and 4 files with indirect coverage changes