Fix compilation, docs and tests

Author: joroKr21

core/src/main/scala/cats/instances/seq.scala

@@ -207,7 +207,7 @@ trait SeqInstances extends cats.kernel.instances.SeqInstances {
   }
 
   implicit def catsStdShowForSeq[A: Show]: Show[Seq[A]] =
-    Show.show(_.iterator.map(Show[A].show).mkString("Seq(", ", ", ")"))
+    Show.show(_.map(Show[A].show).toString)
 
   implicit def catsStdNonEmptyParallelForSeqZipSeq: NonEmptyParallel.Aux[Seq, ZipSeq] =
     new NonEmptyParallel[Seq] {

docs/typeclasses/invariantmonoidal.md

@@ -27,7 +27,7 @@ def unit: Semigroup[Unit] =
   Semigroup.instance((_, _) => ())
 
 def product[A, B](fa: Semigroup[A], fb: Semigroup[B]): Semigroup[(A, B)] =
-  Semigroup.instances { case ((xa, xb), (ya, yb)) =>
+  Semigroup.instance { case ((xa, xb), (ya, yb)) =>
     fa.combine(xa, ya) -> fb.combine(xb, yb)
   }
 ```

free/src/test/scala/cats/free/FreeTSuite.scala

@@ -302,9 +302,9 @@ trait FreeTSuiteInstances {
     override def map[A, B](fa: JustFunctor[A])(f: A => B): JustFunctor[B] = JustFunctor(f(fa.a))
   }
 
-  implicit def freeTOptionEq[A](implicit A: Eq[A], OM: Monad[Option]): Eq[FreeTOption[A]] =
+  implicit def freeTOptionEq[A](implicit A: Eq[A]): Eq[FreeTOption[A]] =
     Eq.by(_.runM(identity))
 
-  implicit def freeTStateEq[A](implicit A: Eq[A], SM: Monad[IntState]): Eq[FreeTState[A]] =
+  implicit def freeTStateEq[A](implicit A: Eq[A]): Eq[FreeTState[A]] =
     Eq.by(_.runM(identity))
 }