fix CSP issue when build on production webpack

[anhdang094]

fix CSP issue when build on production webpack

fix: unsafe-eval by using devtool: source-map

nhn/toast-ui.react-image-editor#30 (comment)

Please check if the PR fulfills these requirements

• It's submitted to right branch according to our branching model
• It's right issue type on title
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)
• It does not introduce a breaking change or has description for the breaking change

[lja1018]

Thanks for the PR.