drop support for Scala.js 0.6

as per scala-js/scala-js#4045

Author: SethTisue

.travis.yml

@@ -12,14 +12,11 @@ scala:
 
 env:
   - ADOPTOPENJDK=8     SCALAJS_VERSION=
-  - ADOPTOPENJDK=8     SCALAJS_VERSION=0.6.33
   - ADOPTOPENJDK=8     SCALAJS_VERSION=1.1.0
   - ADOPTOPENJDK=11    SCALAJS_VERSION=
 
 matrix:
   exclude:
-    - scala: 0.24.0-RC1
-      env: ADOPTOPENJDK=8     SCALAJS_VERSION=0.6.33
     - scala: 0.24.0-RC1
       env: ADOPTOPENJDK=8     SCALAJS_VERSION=1.1.0
   include:

project/plugins.sbt

@@ -1,5 +1,5 @@
 val scalaJSVersion =
-  Option(System.getenv("SCALAJS_VERSION")).filter(_.nonEmpty).getOrElse("0.6.33")
+  Option(System.getenv("SCALAJS_VERSION")).filter(_.nonEmpty).getOrElse("1.1.0")
 
 val scalaNativeVersion =
   Option(System.getenv("SCALANATIVE_VERSION")).filter(_.nonEmpty).getOrElse("0.3.9")