Merge pull request #859 from arduino/Kristoffer-fix

After feedback from @per1234 and a review by @karlsoderby I'm merging this.

Author: kengdahl

Diff for: Language/Variables/Data Types/String/Functions/length.adoc

@@ -34,7 +34,7 @@ Returns the length of the String, in characters. (Note that this doesn't include
 
 [float]
 === Returns
-The length of the String in characters.
+The length of the String in characters. Data type: `unsigned int`.
 
 --
 // OVERVIEW SECTION ENDS