use webpack terser plugin

[shoota]

TL;DR

Replace UglifyJS plugin to Terser Plugin

Check this pr.

How to check

• checkout this pr.
• yarn install && yarn build
• yarn lint

Check list

• [x] passed build and lint

[codecov[bot]]

Codecov Report

Merging #948 into master will increase coverage by 0.15%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #948      +/-   ##
==========================================
+ Coverage    91.5%   91.66%   +0.15%     
==========================================
  Files          25       25              
  Lines         636      636              
  Branches      112      112              
==========================================
+ Hits          582      583       +1     
  Misses         30       30              
+ Partials       24       23       -1

Impacted Files	Coverage Δ
packages/agent/src/core.ts	92.48% <0%> (+0.75%)	:arrow_up: