added sbtserver linter

test/scala_fixtures/invalid_sbt_project/Main.scala

@@ -0,0 +1,5 @@
+object HelloAle {
+  def main(args: Array[String]): Int = {
+    println("Hello, ale!")
+  }
+}

test/scala_fixtures/invalid_sbt_project/project/build.properties

@@ -0,0 +1 @@
+sbt.version=1.2.1

test/scala_fixtures/invalid_sbt_project/project/target/active.json

@@ -0,0 +1 @@
+{"uri":"tcp://127.0.0.1:5211"}