Run demo on new typescript

[anp]

Not a particularly useful PR, but when attempting to run the demo locally the semver bound in package.json allows TypeScript 2.6.1 to be installed, which seems to break the client demo build:

ERROR in ./src/text.ts
(251,23): error TS2345: Argument of type '{ body: string; headers: { 'Content-Type': string; }; method: string;}' is not assignable to parameter of type 'RequestInit | undefined'.
  Type '{ body: string; headers: { 'Content-Type': string; }; method: string; }' is not assignable to type 'RequestInit'.
    Types of property 'headers' are incompatible.
      Type '{ 'Content-Type': string; }' is not assignable to type 'Headers | string[][] | undefined'.
        Object literal may only specify known properties, and ''Content-Type'' does not exist in type 'Headers | string[][] | undefined'.

ERROR in ./src/text.ts
(253,17): error TS7006: Parameter 'response' implicitly has an 'any' type.

ERROR in ./src/text.ts
(256,17): error TS7006: Parameter 'buffer' implicitly has an 'any' type.

ERROR in ./src/svg-loader.ts
(110,23): error TS2345: Argument of type '{ body: string; headers: { 'Content-Type': string; }; method: string;}' is not assignable to parameter of type 'RequestInit | undefined'.
  Type '{ body: string; headers: { 'Content-Type': string; }; method: string; }' is not assignable to type 'RequestInit'.
    Types of property 'headers' are incompatible.
      Type '{ 'Content-Type': string; }' is not assignable to type 'Headers | string[][] | undefined'.
        Object literal may only specify known properties, and ''Content-Type'' does not exist in type 'Headers | string[][] | undefined'.

ERROR in ./src/svg-loader.ts
(112,17): error TS7006: Parameter 'response' implicitly has an 'any' type.

ERROR in ./src/svg-loader.ts
(115,17): error TS7006: Parameter 'buffer' implicitly has an 'any' type.

I also added yarn.lock to gitignore since the README recommends npm, but would be happy to revert.

I suspect that resolving the TS errors with more accurate type defs might be more reasonable, but this allowed me to run the demo on a fresh clone.

[Bobo1239]

This is microsoft/TypeScript#19656 whose fix isn't in a release yet. If you switch typescript's version to next in package.json it builds without errors.

[anp]

Oh, fantastic!

[whmountains]

Don't close, we need the fix.

[anp]

Really? Presumably the TS changes will release soon?

[pcwalton]

I'm confused :)

[anp]

from irc if anyone's following along here:

4:14 PM <dikaiosune> pcwalton: so am i
4:15 PM <•pcwalton> dikaiosune: I’m going to keep the PR open in case MS releases a new version soon
4:15 PM <•pcwalton> if not, then I’ll merge it

[pcwalton]

2578298 includes this.