Deprecation release

2.0.0-beta.21

Merge branch 'master' of github.com:api-ai/apiai-javascript-client

Compatibility features

2.0.0-beta.20

[*] version update to beta-20 + rebuild

2.0.0-beta.18

[*] dependencies update

2.0.0-beta.16

[*] some linting (ionic2 compatibility issues)

2.0.0-beta.15: [*] minor readme updates, + updating version due to fixes of other co…

…ntributor, + exporting Constants, + rebuild libs