fix(package.json): add entry point main for node packaging

[sahil143]

Issue:

With ngx-widgets version 3.1.2(#156) the directory structure changed for published package which caused the following error in planner

{ Error: /home/sbudhwar/node_modules/ngx-widgets/index.js: Couldn't find preset "env" relative to directory "/home/sbudhwar/node_modules/ngx-widgets"
Transform function: 

function (context, callback) {
        if (!context.js) {
            return callback(undefined, false);
        }
        if (isEs6(context.js.ast)) {
            options.filename = context.filename;
            log.debug("Transforming %s", options.filename);
            try {
                context.source = babel.transform(context.source, options).code;
                context.js.ast = acorn.parse(context.source, { sourceType: "module" });
                return callback(undefined, true);
            }
            catch (error) {
                return callback(error, false);
            }
        }
        else {
            return callback(undefined, false);
        }
    }

    at Transformer.handleError (/home/sbudhwar/fabric8/fabric8-planner/node_modules/karma-typescript/src/bundler/transformer.ts:103:19)
    at /home/sbudhwar/fabric8/fabric8-planner/node_modules/karma-typescript/src/bundler/transformer.ts:87:26
    at transform (/home/sbudhwar/fabric8/fabric8-planner/node_modules/karma-typescript-es6-transform/src/transform.ts:69:24)
    at /home/sbudhwar/fabric8/fabric8-planner/node_modules/karma-typescript/src/bundler/transformer.ts:86:17
    at _combinedTickCallback (internal/process/next_tick.js:131:7)
    at process._tickDomainCallback (internal/process/next_tick.js:218:9)
  domain: 
   Domain {
     domain: null,
     _events: {},
     _eventsCount: 0,
     _maxListeners: undefined,
     members: [] }

Cause:

main property was missing from the package.json which caused the node to look for an entry point in the root directory and because of the change in directory structure the entry point for the package resides in src/app/index.js

Solution:

Add main property in package.json with correct entry point

[nimishamukherjee]

Tried this with ng6 planner. Unit tests pass now.

[fabric8cd]

🎉 This PR is included in version 3.1.4 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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