Upgrade the Scalatex readme to Scala 2.12.8.

And optimize the Travis matrix so that we do not redo the readme
build for every version of Scala.

Author: sjrd

.travis.yml

@@ -3,7 +3,6 @@ language: scala
 script:
   - sbt ++$TRAVIS_SCALA_VERSION package doc example/compile
   - sbt scalafmtTest
-  - sbt ++2.11.12 readme/run
 scala:
   - 2.10.7
   - 2.11.12
@@ -18,6 +17,11 @@ matrix:
   exclude:
     - scala: 2.10.7
       env: SCALAJS_VERSION=1.0.0-M7
+  include:
+    - scala: 2.12.8
+      env: SCALAJS_VERSION=0.6.27
+      script:
+        - sbt readme/run
 
 cache:
   directories:

build.sbt

@@ -111,7 +111,7 @@ lazy val readme = ScalatexReadme(
   source = "Index",
   autoResources = Seq("example-opt.js")
 ).settings(
-  scalaVersion := "2.11.12",
+  scalaVersion := "2.12.8",
   scalacOptions ++= Seq("-deprecation", "-feature", "-Xfatal-warnings"),
   (resources in Compile) += (fullOptJS in (example, Compile)).value.data
 )