fix(generate-schema): load typescript files properly

[FRSgit]

start using same load module everywhere

When starting new vue-apollo typescript project I've found out that vue-cli-service apollo:schema:generate command fails with error ERROR Error: Cannot find module '/Users/jakubfreisler/Projects/Web/scrabbio/apollo-server/type-defs' when type-defs file got ts extension (with js file everything've worked as expected).
Also, at the same time, vue-cli-service apollo:dev was working (which I was weird for me).

So, after some investigation I found out that:

• index.js and utils/generate-schema.js modules are using copy-pasted implementation of load function, but placed in two different places in the codebase (one was directly in index.js file, second one in utils/load.js),
• implementation of load function which was available within utils/load.js module was not working with typescript files (raised the error above).

First of all I've pointed both index.js and utils/generate-schema.js to use the same load function from utils/load.js.

Then, I've figured out that this function was never working with typescript files properly because ts-node/register/transpile-only module was never required in the context of the file utils/load.js. The same load implementation contained in index.js have worked before, because ts-node/register/transpile-only module was required in the index.js before load function was used (and load function was in the same file = in the same context). And in case of utils/load the ts-node/register/transpile-only was always required in the file which required also utils/load.js (but never in utils/load.js itself).

Fix was quite easy - I've just moved require('ts-node/register/transpile-only') to the utils/load.js. This change fixed the problem and de-duplicated codebase a bit.

@Akryum do you want me to do any additional work before this PR could be merged?

[FRSgit]

Thx for merging this one! ❤️