./bin/init script sed syntax not compatible with Linux sed

[RobertoMaurizzi]

I'm trying to learn React Native and this repo is really interesting, thank you! :-)

I'm on Linux and sed short parameters here must not have a space following them. In ./bin/init sed invocations like:

sed -E -i '' "s/ext.appName = \"[^\"]*\"/ext.appName = \"$appname\"/g" ./android/app/build.gradle

should be:

sed -E -i'' "s/ext.appName = \"[^\"]*\"/ext.appName = \"$appname\"/g" ./android/app/build.gradle

Notice the lack of a space after -i

Not a PR because I'm not sure if that syntax is accepted on OSX 😄