modernise the dependencies

deprecate node 10.x

prepare release 0.2.18 (#35)

* add github actions
* bump up the version

Merge pull request #26 from baxtree/development

add microsoft extension of vxml and fix style degree

Merge pull request #23 from baxtree/development

add more optional values and attributes

Merge pull request #22 from baxtree/development

update dependencies

Merge pull request #21 from baxtree/development

add doctype for ssml 1.0 and parameterise encoding

Merge pull request #19 from baxtree/development

support lexicon, amazon:max-duration and amazon:domain conversational style and fix google media begin/end time

Merge pull request #19 from baxtree/development

support lexicon, amazon:max-duration and amazon:domain conversational style and fix google media begin/end time

bump up the version for a new release