bug: AxiosRequestConfig.proxy should allow type false

[dhcmrlchtdj]

#### Summary

I can't create an instance with axios.create({proxy: false}).
tsc report

error TS2345: Argument of type '{ proxy: boolean; }' is not assignable to parameter of type 'AxiosRequestConfig | undefined'.
  Type '{ proxy: boolean; }' is not assignable to type 'AxiosRequestConfig'.
    Types of property 'proxy' are incompatible.
      Type 'boolean' is not assignable to type 'AxiosProxyConfig | undefined'.

The typing should be AxiosProxyConfig | false, however false is missing at current version.

axios/index.d.ts

Line 43 in fbb5d4d

proxy?: AxiosProxyConfig;

axios/lib/adapters/http.js

Line 85 in fbb5d4d

if (!proxy && proxy !== false) {

#### Context

• axios version: v0.17.0

[nickuraltsev]

Right! I'd be happy to accept a PR.

[nickuraltsev]

Fixed via #1177