update version of gettext-parser requirement

[RignonNoel]

Thanks for this great lib! Usage of PO file is a great enhancement!

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Fix issue #22 since it was related to an issue of gettext-parser.

I already made a fix that has been released on the dependency so we just need to upgrade to the new version.

Special note:

Since my fix on gettext-parser was linked to a limitation of old nodejs version we have two new version of gettext-parser (V2.x and V3.x), i decided to put the v2 in this PR to support old node version since this lib is really short in code.

Analyse of breaking changes:

From 1.x to 2.x we have only one breaking change:

BREAKING: sortByMsgId parameter was renamed to sort

But we don't use this function in this library, so we can upgrade easily :)

[LizanLycan]

With Angular 7 compiles, but when running in the browser:

Uncaught ReferenceError: process is not defined
    at Object../node_modules/@biesbjerg/ngx-translate-po-http-loader/node_modules/process-nextick-args/index.js (index.js:3)
    at __webpack_require__ (bootstrap:78)
    at Object../node_modules/@biesbjerg/ngx-translate-po-http-loader/node_modules/readable-stream/lib/_stream_readable.js (_stream_readable.js:26)
    at __webpack_require__ (bootstrap:78)
    at Object../node_modules/@biesbjerg/ngx-translate-po-http-loader/node_modules/readable-stream/readable-browser.js (readable-browser.js:1)
    at __webpack_require__ (bootstrap:78)
    at Object../node_modules/@biesbjerg/ngx-translate-po-http-loader/node_modules/gettext-parser/lib/poparser.js (poparser.js:5)
    at __webpack_require__ (bootstrap:78)
    at Object../node_modules/@biesbjerg/ngx-translate-po-http-loader/node_modules/gettext-parser/index.js (index.js:3)
    at __webpack_require__ (bootstrap:78)

I change the dependency in package.json and run npm install for this gettext but doesn't work.

[RignonNoel]

@LizanLycan I didn't found information about angular official support of NodeJS version, do you know a link about it ?

I think that maybe Angular7 drop some NodeJS version and that you need to user gettext v3 as i described in my PR. (I really don't know it's just a first fast guess, i don't have the time to check that right now)

[LizanLycan]

Well, since the original problem of the error was by dependencies of the gettext, I saw that everything came from its dependency with stream, so it is not necessary to update the version, it is an error of the CLI Angular that since version 6 is presenting (see comment about it: #29 (comment))