Added comments suggestions and ScalaTest 3.1.0 update

Author: kiroco12

src/test/scala/com/fortysevendeg/exercises/ExampleTarget.scala

@@ -19,9 +19,10 @@
 
 package org.scalaexercises.runtime
 
-import org.scalatest._
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
 
-object ExampleTarget extends FlatSpec with Matchers {
+object ExampleTarget extends AnyFlatSpec with Matchers {
   def intStringMethod(a: Int, b: String): String =
     s"$a$b"
 

src/test/scala/com/fortysevendeg/exercises/LibraryDiscoverySpec.scala

@@ -21,9 +21,10 @@ package org.scalaexercises.runtime
 
 import org.scalaexercises.runtime.model.Exercise
 
-import org.scalatest._
+import org.scalatest.funspec.AnyFunSpec
+import org.scalatest.matchers.should.Matchers
 
-class LibraryDiscoverySpec extends FunSpec with Matchers {
+class LibraryDiscoverySpec extends AnyFunSpec with Matchers {
 
   import org.scalaexercises.content._
 

src/test/scala/com/fortysevendeg/exercises/TimestampSpec.scala

@@ -19,9 +19,10 @@
 
 package org.scalaexercises.runtime
 
-import org.scalatest._
+import org.scalatest.funspec.AnyFunSpec
+import org.scalatest.matchers.should.Matchers
 
-class TimestampSpec extends FunSpec with Matchers {
+class TimestampSpec extends AnyFunSpec with Matchers {
   describe("Timestamp") {
     it("works in both directions") {
       val date = new java.util.Date()