Bump uglifier from 4.1.9 to 4.2.0

Bumps uglifier from 4.1.9 to 4.2.0.

Changelog

Sourced from uglifier's changelog.

4.2.0 (25 September 2019)

• show code context for error messages (#167)
• defer initialisation of ExecJS context to fix #165

4.1.20 (17 November 2018)

• update UglifyJS to 3.4.8

4.1.19 (11 September 2018)

• update UglifyJS to 3.4.9

4.1.18 (09 August 2018)

• update UglifyJS to 3.4.7

4.1.17 (29 July 2018)

• update UglifyJS to 3.4.6

4.1.16 (22 July 2018)

• update UglifyJS to 3.4.5

4.1.15 (13 July 2018)

• update UglifyJS to 3.4.4

4.1.14 (02 July 2018)

• update UglifyJS to 3.4.3

4.1.13 (30 June 2018)

• update UglifyJS to 3.4.2

4.1.12 (20 June 2018)

• update UglifyJS to 3.4.1

4.1.11 (02 June 2018)

• update UglifyJS to 3.3.28

4.1.10 (21 April 2018)

• update UglifyJS to 3.3.22

Commits

• 77226d1 Bump version to 4.2.0
• ac86e3e Update changelog
• 18f0419 Ignore Rubocop warning
• 3ff23bb Use new GitHub actions syntax
• 116444d Handle unexpected error messages better
• 9de67eb Defer initialisation of ExecJS context
• 990a6eb Expand abbreviations in variable names
• 4f65798 Refactor error context line option handling
• 5e544f5 Fix typo in method name
• 9958a20 Merge pull request #167 from eGust/err-context-lines
• Additional commits viewable in compare view