Update core.js

[pomelio]

add a CommentBlock before the statement
for example:
squel.select().comment('writeHost').from('user); => /* writeHost */ SELECT * from user;

[codecov]

Codecov Report

Merging #356 into master will decrease coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #356      +/-   ##
==========================================
- Coverage   81.31%   81.15%   -0.16%     
==========================================
  Files           2        2              
  Lines        2863     2887      +24     
  Branches      635      639       +4     
==========================================
+ Hits         2328     2343      +15     
- Misses        535      544       +9

Impacted Files	Coverage Δ
dist/squel.js	72.06% <0%> (-0.23%)	⬇️
dist/squel-basic.js	93.29% <0%> (-0.1%)	⬇️

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