Fix import paths in adapters

[hashedhyphen]

Type of change

Bugfix

Description of change

This PR fixes issues when importing some adapters as npm dependencies.

Source:

import 'prebid.js/modules/open8BidAdapter';

Webpack's output:

ERROR in ./node_modules/prebid.js/modules/open8BidAdapter.js
Module not found: Error: Can't resolve 'src/utils' in '/path/to/node_modules/prebid.js/modules'
 @ ./node_modules/prebid.js/modules/open8BidAdapter.js 3:0-35 27:20-43 28:20-46 29:20-46 91:28-54 95:10-24 159:4-17

After this change, I confirmed npm test passed locally.

> npm test
...
Finished in 3.45 secs / 1.537 secs @ 18:39:56 GMT+0900 (GMT+09:00)

SUMMARY:
✔ 3959 tests completed
ℹ 1 test skipped
[18:39:56] Finished 'test' after 28 s
[18:39:56] Finished 'test' after 43 s

[jsnellbaker]

@hashedhyphen Thanks for putting this together.