[wct-browser-legacy] Updated @webcomponents/webcomponentsjs dependency to ^2.0.0 from ^1.0.7

[usergenic]

This is a RELEASE PR for wct-browser-legacy 1.0.1

Addressing an oversight that it should have been released with @webcomponents/webcomponentsjs v2 already.

[usergenic]

I'm going to package and test this locally with some elements to see if there are issues.

[usergenic]

 ~/s/s/wc2-test  npm install ~/src/github.com/polymer/tools~wct-browser-legacy/packages/web-component-tester/wct-browser-legacy/wct-browser-legacy-1.0.1.tgz
npm notice created a lockfile as package-lock.json. You should commit this file.
npm WARN wc2-test@ No description
npm WARN wc2-test@ No repository field.
npm WARN wc2-test@ No license field.

+ wct-browser-legacy@1.0.1
removed 1 package and updated 1 package in 4.047s
[+] no known vulnerabilities found [26 packages audited]

 ~/s/s/wc2-test  npm ls wct-browser-legacy
wc2-test@ /Users/usergenic/src/scratch/wc2-test
└── wct-browser-legacy@1.0.1

 ~/s/s/wc2-test  npm ls @webcomponents/webcomponentsjs
wc2-test@ /Users/usergenic/src/scratch/wc2-test
├── @webcomponents/webcomponentsjs@2.0.0
└─┬ wct-browser-legacy@1.0.1
  └── @webcomponents/webcomponentsjs@2.0.0  deduped

 ~/s/s/wc2-test  polymer test
Installing and starting Selenium server for local browsers
Selenium server running on port 55761
[BABEL] Note: The code generator has deoptimised the styling of undefined as it exceeds the max of 500KB.
[BABEL] Note: The code generator has deoptimised the styling of undefined as it exceeds the max of 500KB.               safari 11.1 ()
safari 11.1              Beginning tests via http://localhost:8081/components/wc2-test/generated-index.html?cli_browser_id=3
safari failed to maximize
[BABEL] Note: The code generator has deoptimised the styling of undefined as it exceeds the max of 500KB.
chrome 66                Beginning tests via http://localhost:8081/components/wc2-test/generated-index.html?cli_browser_id=1
chrome failed to maximize
firefox 59               Beginning tests via http://localhost:8081/components/wc2-test/generated-index.html?cli_browser_id=2
chrome 68                Beginning tests via http://localhost:8081/components/wc2-test/generated-index.html?cli_browser_id=0
chrome failed to maximize
safari 11.1              Tests passed
firefox 59               Tests passed
chrome 68                Tests passed
chrome 66                Tests passed
Test run ended with great success

chrome 68 (2/0/0)                       chrome 66 (2/0/0)                       firefox 59 (2/0/0)                      safari 11.1 (2/0/0)

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Note to above comment, demonstrates this change doesn't break "the simple case" i.e. a fresh element's tests.