Use scala 2.13.0-M4 milestone release

Author: ashawley

.travis.yml

@@ -16,7 +16,7 @@ jdk:
 scala:
   - 2.11.12
   - 2.12.6
-  - 2.13.0-M3
+  - 2.13.0-M4
 
 env:
   global:
@@ -46,7 +46,7 @@ matrix:
       jdk: openjdk11
     - scala: 2.12.6
       jdk: openjdk6
-    - scala: 2.13.0-M3
+    - scala: 2.13.0-M4
       jdk: openjdk6
 
 script: 

build.sbt

@@ -1,7 +1,7 @@
 import sbtcrossproject.{crossProject, CrossType}
 import ScalaModulePlugin._
 
-crossScalaVersions in ThisBuild := List("2.12.6", "2.11.12", "2.13.0-M3")
+crossScalaVersions in ThisBuild := List("2.12.6", "2.11.12", "2.13.0-M4")
 
 lazy val xml = crossProject(JSPlatform, JVMPlatform)
   .withoutSuffixFor(JVMPlatform)
@@ -27,7 +27,7 @@ lazy val xml = crossProject(JSPlatform, JVMPlatform)
       (unmanagedSourceDirectories in Compile).value.map { dir =>
         val sv = scalaVersion.value
         CrossVersion.partialVersion(sv) match {
-          case Some((2, 13)) if !sv.startsWith("2.13.0-M3") => file(dir.getPath ++ "-2.13") // TODO: remove M3 guard once M4 is out.
+          case Some((2, 13)) => file(dir.getPath ++ "-2.13")
           case _             => file(dir.getPath ++ "-2.11-2.12")
         }
       }