Small fixes

Author: Sporarum

docs/_spec/06-expressions.md

@@ -967,7 +967,7 @@ x => x                             // The identity function
 
 f => g => x => f(g(x))             // Curried function composition
 
-(x: Int,y: Int) => x + y           // A summation function
+(x: Int, y: Int) => x + y          // A summation function
 
 () => { count += 1; count }        // The function which takes an
                                    // empty parameter list ´()´,

docs/_spec/12-the-scala-standard-library.md

@@ -621,7 +621,7 @@ object Predef {
 
   def assume(assumption: Boolean, message: => Any) {
     if (!assumption)
-      throw new IllegalArgumentException(message.toString)
+      throw new IllegalArgumentException("assumption failed: " + message.toString)
   }
 
   def require(requirement: Boolean) {