Update base version

Author: nicolasstucki

project/Build.scala

@@ -57,7 +57,7 @@ object MyScalaJSPlugin extends AutoPlugin {
 object Build {
   val referenceVersion = "3.0.0-RC1-bin-20210122-6947b0f-NIGHTLY"
 
-  val baseVersion = "3.0.0-RC1"
+  val baseVersion = "3.0.0-M4"
   val baseSbtDottyVersion = "0.5.3"
 
   // Versions used by the vscode extension to create a new project