Update scripts to work with 1.39 and earlier Theia releases #170

[jfaltermeier]

• rebuild needs to be run performed before build

Steps to reproduce issues with released version of generator

mkdir my-extension-38 && cd my-extension-38
yo theia-extension -t 1.38.0
<Enter> (Hello World extension type)
<Enter> (hello-world extension name)
yarn start:browser
yarn start:electron

mkdir my-extension-39 && cd my-extension-39
yo theia-extension -t 1.39.0
<Enter> (Hello World extension type)
<Enter> (hello-world extension name)
yarn start:browser
yarn start:electron

Steps to test including fixes in this PR:

mkdir my-extension-38 && cd my-extension-38
yo theia-extension -t 1.38.0
<Enter> (Hello World extension type)
<Enter> (hello-world extension name)
yarn build:browser
yarn start:browser
yarn build:electron
yarn start:electron

mkdir my-extension-39 && cd my-extension-39
yo theia-extension -t 1.39.0
<Enter> (Hello World extension type)
<Enter> (hello-world extension name)
yarn build:browser
yarn start:browser
yarn build:electron
yarn start:electron

[vince-fugnitto]

I can confirm the updated instructions work as expected 👍