Tab completion is broken by default

[bijancn]

When I just add the plugin and type dock and TAB, I get

java.lang.RuntimeException: ./ ./ dockerComposeIgnore is undefined.
        at scala.sys.package$.error(package.scala:27)
        at sbt.Extracted.$anonfun$getOrError$1(Extracted.scala:119)
        at scala.Option.getOrElse(Option.scala:121)
        at sbt.Extracted.getOrError(Extracted.scala:119)
        at sbt.Extracted.getOrError(Extracted.scala:124)
        at sbt.Extracted.get(Extracted.scala:34)
        at com.github.ehsanyou.sbt.docker.compose.parsers.package$.$anonfun$dockerComposeTestParser$2(package.scala:52)
        at sbt.InputTask$.$anonfun$free$1(InputTask.scala:74)
        at sbt.InputTask.$anonfun$mapTask$1(InputTask.scala:19)
        at sbt.std.ParserInstance$.$anonfun$map$2(TaskMacro.scala:50)
        at sbt.InputTask.$anonfun$mapTask$1(InputTask.scala:19)
        at sbt.internal.Aggregation$.$anonfun$applyDynamicTasks$2(Aggregation.scala:164)
        at scala.collection.TraversableLike$WithFilter.$anonfun$map$2(TraversableLike.scala:739)
        at scala.collection.immutable.List.foreach(List.scala:389)
        at scala.collection.TraversableLike$WithFilter.map(TraversableLike.scala:738)
        at sbt.internal.Aggregation$.applyDynamicTasks(Aggregation.scala:163)
        at sbt.internal.Aggregation$.evaluatingParser(Aggregation.scala:205)
        at sbt.internal.Act$.evaluate$1(Act.scala:431)
        at sbt.internal.Act$.$anonfun$actParser0$6(Act.scala:440)
        at sbt.internal.util.complete.BindParser.$anonfun$completions$3(Parser.scala:735)
        at sbt.internal.util.complete.Completions.$anonfun$flatMap$2(Completions.scala:28)
        at scala.collection.TraversableLike.$anonfun$flatMap$1(TraversableLike.scala:241)
        at scala.collection.immutable.HashSet$HashSet1.foreach(HashSet.scala:320)
        at scala.collection.immutable.HashSet$HashTrieSet.foreach(HashSet.scala:976)
        at scala.collection.immutable.HashSet$HashTrieSet.foreach(HashSet.scala:976)
        at scala.collection.TraversableLike.flatMap(TraversableLike.scala:241)
        at scala.collection.TraversableLike.flatMap$(TraversableLike.scala:238)
        at scala.collection.AbstractTraversable.flatMap(Traversable.scala:104)
        at sbt.internal.util.complete.Completions.$anonfun$flatMap$1(Completions.scala:28)
        at sbt.internal.util.complete.Completions$$anon$1.get$lzycompute(Completions.scala:42)
        at sbt.internal.util.complete.Completions$$anon$1.get(Completions.scala:42)
        at sbt.internal.util.complete.Completions.$anonfun$$plus$plus$1(Completions.scala:20)
        at sbt.internal.util.complete.Completions$$anon$1.get$lzycompute(Completions.scala:42)

(tested on 1.0.0 as 1.1.0 is not published)