Delete ignored files from repository

[nomaed]

1. While lib/* is specified in .gitignore, the directory is actually committed to the repository. This commit deletes these files (which are automatically generated upon build), so that there's less noise while working on the project.

2. Since compiled files are needed for tests, also added build stage before running mocka, to make sure that we have those in travis pipelines.

   // package.json 
   ...
   "scripts": {
   "build": "tsc -p .",
   "test": "tsc -p . && mocha -u tdd --timeout 60000",
   "gitbook": "gitbook build docs"
   },

3. TypeScript wasn't able to build the package because of 3 errors. These have been fixed. No functionality should be affected, these are only syntactic modifications

src/install/bin.ts added @ts-ignore, TS wouldn't compile since function is currently not being used:

// @ts-ignore
function isCygwin () {
...

src/install/fetch.ts modified import:

// from:
import HttpsProxyAgent from 'https-proxy-agent';
// to
import * as HttpsProxyAgent from 'https-proxy-agent';

src/api.ts changed property access to use map access since stack is not defined as a valid property of err's type:

    // from:
    logErr(err.stack || err);
    // to:
    logErr(err['stack'] || err);