Fix REPL not failing where real code would fail by removing :fail and…

… adding a comment

docs/src/main/tut/typeclasses/imports.md

@@ -41,10 +41,10 @@ o.orEmpty
 ```
 
 If you'd like to import à la carte, you can do so, by importing from `cats.instances` for the type class instances and `cats.syntax` for syntax enrichment.
-For example, if you'd like to import the `Semigroup` instance for `String` and the corresponding syntax:
+For example, if you'd like to import the `Monoid` instance for `String` and the corresponding syntax:
 ```tut:book
 import cats.instances.string._
-import cats.syntax.semigroup._
+import cats.syntax.monoid._
 
 "Hello, " |+| "World!"
 ```
@@ -66,14 +66,14 @@ NonEmptyList.of(1,2) <+> NonEmptyList.of(3,4)
 **Note**: Beware that if you import a type class instance or its syntax twice, you will receive conflicting implicits with a less than helpful error message.
 This usually happens when importing different type classes in the same hierarchy or when importing syntax enrichment for all type classes using `cats.syntax.all._` or `cats.implicits._` together with a more specific import like `cats.syntax.option._` or `cats.instances.either._`.
 Below is an example of this phenomenon:
-```tut:fail
+```tut:silent
 import cats.instances.all._
 import cats.syntax.semigroup._
 val x = -2 |+| 1
 
 //now we also need access to isEmpty from Monoid
 import cats.syntax.monoid._
-(x |+| 1).isEmpty
+(x |+| 1).isEmpty //error: value |+| is not a member of Int
 ```
 
 Compilation fails on the second invocation of `|+|` because we now have conflicting implicits from `Monoid` and `Semigroup`.