Changed most Dotty references to Scala 3

[alvinj]

I just used this template and noticed that it still references Dotty in several places, so I updated those. I also modified the README slightly.

Also, I didn’t know how to test this code, so please consider it untested.

[SethTisue]

tested post-merge:

~ % sbt new scala/scala3.g8
[info] welcome to sbt 1.4.4 (AdoptOpenJDK Java 1.8.0_275)
[info] loading global plugins from /Users/tisue/.sbt/1.0/plugins
[info] set current project to tisue (in build file:/Users/tisue/)
[info] set current project to tisue (in build file:/Users/tisue/)

A template to demonstrate a minimal Scala 3 application 

name [Scala 3 Project Template]: foo

Template applied in /Users/tisue/./foo
~ % cd foo
README.md  build.sbt  project/   src/
~/foo % less build.sbt 
~/foo % sbt run
[info] welcome to sbt 1.4.4 (AdoptOpenJDK Java 1.8.0_275)
[info] loading global plugins from /Users/tisue/.sbt/1.0/plugins
[info] loading settings for project foo-build from plugins.sbt ...
[info] loading project definition from /Users/tisue/foo/project
[info] loading settings for project root from build.sbt ...
[info] set current project to scala3-simple (in build file:/Users/tisue/foo/)
[info] compiling 1 Scala source to /Users/tisue/foo/target/scala-3.0.0-M2/classes ...
[info] running Main$package 
Hello world!
I was compiled by Scala 3. :)
[success] Total time: 3 s, completed Dec 13, 2020 6:56:17 PM

[alvinj]

Thanks! And now I know how to test it! :)