add typescript as a peer dependency

[punmechanic]

This will prevent issues like #226 and #229 from being raised again
(hopefully).

awesome-typescript-loader 2.2.3 onwards broke
compatibility with TypeScript 2.0 and some people (including myself)
depended on it. Unfortunately, it failed silently, leaving a rather
cryptic error. TypeScript's dependency was updated as a devDependency on
this package to 2.0.2, however TypeScript itself has never been
installed as a peerDependency.

Adding TypeScript as a peerDependency will alert consumers of this
package when they install a version of TypeScript that is not supported
by this plugin.

Of course, perhaps >= 2.0.2 is too weak a constraint, but it's better
than none.

Here's what will be displayed if you install a version below the required version (in this example I installed TypeScript 2.0.0)

[punmechanic]

There seems to be a bug with your CI runner and Babel plugins. :( that CI failure has nothing to do with this change.

Note that you may wish to alter the peerDependency version (I'm not sure what versions you support).

[punmechanic]

Hey @s-panferov, I'm glad you fixed the issue, but a little disappointed you merged a PR by an existing contributor (#536) and closed this PR without saying anything.

In future I'd encourage you to leave feedback on why a specific PR wasn't merged (especially as it has been open for so long).

I understand it's a trivial fix, but it does feel kinda bad :)

[s-panferov]

@danpantry sorry for this. I have very limited time to maintain this project and it was just easier for me to merge more common request. This fix appeared quite trivial to me to accept the easy path. Thanks for your contribution anyway!