add optional proxy config property

This is passed through to axios to allow the full range of proxy config and override capability.

By default axios looks at environment variables http_proxy and https_proxy to determine if proxy should be used. If these are not set then it will default off.

To force axios to not use the env variables, use `proxy: false`

To force different proxy values (overriding env variables) provide an object compatible with axios like

```js
proxy: {
  host: '127.0.0.1',
    port: 9000,
    auth: {
      username: 'mikeymike',
      password: 'rapunz3l'
    }
}
```

See https://github.com/axios/axios#config-defaults for full details about what is allowed by axios.

README.md

@@ -174,6 +174,17 @@ var opts = {
     /* strings or binaries */
   ],
   passphrase: 'yourpassphrase',
+  proxy: false /* OR proxy config as defined in axios.
+  If not set axios detects proxy from env vars http_proxy and https_proxy
+  https://github.com/axios/axios#config-defaults
+  {
+    host: '127.0.0.1',
+    port: 9000,
+    auth: {
+      username: 'mikeymike',
+      password: 'rapunz3l'
+    }
+  } */,
   auth: {
     user: 'theuser', // or username
     pass: 'thepassword', // or password

lib/wait-on.js

@@ -43,12 +43,12 @@ const WAIT_ON_SCHEMA = Joi.object({
   cert: [Joi.string(), Joi.binary()],
   key: [Joi.string(), Joi.binary(), Joi.object()],
   passphrase: Joi.string(),
+  proxy: [Joi.boolean(), Joi.object()],
   auth: Joi.object({
     username: Joi.string(),
     password: Joi.string(),
   }),
   strictSSL: Joi.boolean().default(false),
-  ignoreProxy: Joi.boolean().default(false),
   followRedirect: Joi.boolean().default(true), // HTTP 3XX responses
   headers: Joi.object(),
 });
@@ -265,10 +265,10 @@ function createHTTP$({ validatedOpts, output }, resource) {
     followRedirect,
     httpTimeout: timeout,
     interval,
+    proxy,
     reverse,
     simultaneous,
     strictSSL: rejectUnauthorized,
-    ignoreProxy,
   } = validatedOpts;
   const method = HTTP_GET_RE.test(resource) ? 'get' : 'head';
   const url = resource.replace('-get:', ':');
@@ -284,9 +284,9 @@ function createHTTP$({ validatedOpts, output }, resource) {
       ...pick(['ca', 'cert', 'key', 'passphrase'], validatedOpts),
     }),
     ...(followRedirect ? {} : { maxRedirects: 0 }), // defaults to 5 (enabled)
+    ...(proxy && { proxy }),
     ...(timeout && { timeout }),
     ...urlSocketOptions,
-    ...(ignoreProxy ? { proxy: false }: {}), // axios no proxy
     method,
     // by default it provides full response object
     // validStatus is 2xx unless followRedirect is true (default)