Fix Capture instances for IO and Future (#195)

cats-effect/js/src/test/scala/github4s/cats/effect/js/CatsEffectJSSpec.scala

@@ -82,7 +82,7 @@ class CatsEffectJSSpec extends AsyncFunSuite with Matchers {
   }
 
   // only here for the 80% coverage, to remove once JS makes use of Captures
-  test("IOCapture == IO.pure") {
-    ioCaptureInstance.capture("a") shouldBe IO.pure("a")
+  test("IOCapture == IO.apply") {
+    ioCaptureInstance.capture("a") shouldBe IO("a")
   }
 }

cats-effect/shared/src/main/scala/github4s/cats/effect/IOCaptureInstance.scala

@@ -21,6 +21,6 @@ import github4s.free.interpreters.Capture
 
 trait IOCaptureInstance {
   implicit val ioCaptureInstance = new Capture[IO] {
-    override def capture[A](a: ⇒ A): IO[A] = IO.pure(a)
+    override def capture[A](a: ⇒ A): IO[A] = IO(a)
   }
 }

github4s/shared/src/main/scala/github4s/Implicits.scala

@@ -19,7 +19,7 @@ package github4s
 import cats.instances.FutureInstances
 import cats.{Eval, FlatMap, Id, Monad, MonadError}
 import github4s.free.interpreters._
-import scala.concurrent.Future
+import scala.concurrent.{Future, ExecutionContext}
 
 object implicits
     extends FutureCaptureInstance
@@ -29,8 +29,8 @@ object implicits
 
 trait FutureCaptureInstance {
   //Future Capture evidence:
-  implicit val futureCaptureInstance = new Capture[Future] {
-    override def capture[A](a: ⇒ A): Future[A] = Future.successful(a)
+  implicit def futureCaptureInstance(implicit ec: ExecutionContext) = new Capture[Future] {
+    override def capture[A](a: ⇒ A): Future[A] = Future(a)
   }
 }