fix: Panic on incomplete escape sequences in regex patterns

[Stranger6667]

Fixes #253

[codecov]

Codecov Report

Merging #268 (6247851) into master (d7b6919) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #268      +/-   ##
==========================================
+ Coverage   82.84%   82.85%   +0.01%     
==========================================
  Files          53       53              
  Lines        4132     4135       +3     
==========================================
+ Hits         3423     3426       +3     
  Misses        709      709              

Impacted Files	Coverage Δ
jsonschema/src/lib.rs	100.00% <100.00%> (ø)

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