[TS][Angular1&2][Node] Extends obj using Object.assign

[damienpontifex]

PR checklist

• Read the contribution guildelines.
• Ran the shell/batch script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates)
• Filed the PR against the correct branch: master for non-breaking changes and 2.3.0 branch for breaking (non-backward compatible) changes.

Description of the PR

Resolves #4407 (replacing PR #4409 with better backwards compatibility) by using Object.assign for object copying.

[wing328]

@damienpontifex thanks for the PR. The CI (travis) failed due to

[INFO] TS Node npm Petstore Client ....................... FAILURE [11.932s]

with the following error messages:

[INFO] 
[INFO] --- exec-maven-plugin:1.2.1:exec (npm-run-build) @ TypeScriptNodeNPMPestoreClientTests ---

> @swagger/[email protected] build /home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/typescript-node/npm
> tsc

client.ts(37,52): error TS2345: Argument of type 'ReadStream' is not assignable to parameter of type 'Buffer'.
  Property 'write' is missing in type 'ReadStream'.

npm ERR! Linux 4.4.0-51-generic
npm ERR! argv "/home/travis/.nvm/versions/node/v4.1.2/bin/node" "/home/travis/.nvm/versions/node/v4.1.2/bin/npm" "run" "build"
npm ERR! node v4.1.2
npm ERR! npm  v2.14.4
npm ERR! code ELIFECYCLE
npm ERR! @swagger/[email protected] build: `tsc`
npm ERR! Exit status 2
npm ERR! 
npm ERR! Failed at the @swagger/[email protected] build script 'tsc'.
npm ERR! This is most likely a problem with the @swagger/angular2-typescript-petstore package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR!     tsc
npm ERR! You can get their info via:
npm ERR!     npm owner ls @swagger/angular2-typescript-petstore
npm ERR! There is likely additional logging output above.

npm ERR! Please include the following file with any support request:
npm ERR!     /home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/typescript-node/npm/npm-debug.log

Ref: https://s3.amazonaws.com/archive.travis-ci.org/jobs/192219854/log.txt

Please take a look when you've time.

[damienpontifex]

Thanks @wing328 just a small node issue. Fixed up and ready for review. Also @todrules might be interested for review

[wing328]

@damienpontifex thanks for the quick fix and this PR looks good to me. Thanks for the enhancement 👍