Improved content parser for .mill-version file

Fix sugested by Frank Thomas.

Author: lefou

modules/core/src/main/scala/org/scalasteward/core/edit/UpdateHeuristic.scala

@@ -215,7 +215,7 @@ object UpdateHeuristic {
         defaultReplaceVersion(_ => List("version"))(update)
       case update: Update.Single if MillAlg.isMillMainUpdate(update) =>
         // this is intended to update the `.mill-version`
-        content => if (content === update.currentVersion) Some(update.nextVersion) else None
+        content => if (content.trim() === update.currentVersion) Some(update.nextVersion) else None
       case _ =>
         _ => None
     }

modules/core/src/test/scala/org/scalasteward/core/edit/EditAlgTest.scala

@@ -258,7 +258,7 @@ class EditAlgTest extends FunSuite {
       newerVersions = Nel.of("0.9.9")
     )
     val original = Map(
-      ".mill-version" -> """0.9.5""",
+      ".mill-version" -> "0.9.5 \n ",
       ".travis.yml" -> """- TEST_MILL_VERSION=0.9.5"""
     )
     val expected = Map(