[BUG] PLAYWRIGHT_BROWSERS_PATH throws error on subsequent installs

[aesyondu]

Context:

• Playwright Version: 0.12.1
• Operating System: Mac OS X 10.14.6
• Extra: [email protected], [email protected]

Code Snippet

$ npm install -D playwright@latest

### NOTE: latest resolves to 0.12.1
# in .bash_profile
# export PLAYWRIGHT_BROWSERS_PATH="$HOME/playwright-browsers"

### stdout & stderr:
npm WARN deprecated [email protected]: Legacy versions of mkdirp are no longer supported. Please update to mkdirp 1.x. (Note that the API surface has changed to use Promises in 1.x.)

> [email protected] install /Users/aes/sandbox/playwright-element-click/node_modules/playwright
> node install.js

(node:25564) UnhandledPromiseRejectionWarning: Error: ERROR: downloadPath folder already exists!
    at Object.downloadBrowser (/Users/aes/sandbox/playwright-element-click/node_modules/playwright-core/lib/server/browserFetcher.js:110:15)
    at async downloadBrowserWithProgressBar (/Users/aes/sandbox/playwright-element-click/node_modules/playwright-core/download-browser.js:65:3)
    at async /Users/aes/sandbox/playwright-element-click/node_modules/playwright/install.js:21:3
(node:25564) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:25564) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
npm WARN [email protected] No description
npm WARN [email protected] No repository field.

+ [email protected]
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found 0 vulnerabilities

Describe the bug

PLAYWRIGHT_BROWSERS_PATH works great, but it throws an error on subsequent installs.

Relevant code here:

playwright/src/server/browserFetcher.ts

Line 145 in ea16e55

throw new Error('ERROR: downloadPath folder already exists!');

EDIT:
Expect not to throw when downloadPath already exists.