Update list methods descriptions

Clarified description for every() and some().

Author: butlermatt

src/site/_includes/language-tour/3-built-in-types/lists.html

@@ -120,8 +120,8 @@ <h4> List and Collection methods </h4>
 returns a new collection with only the elements that satisfy a condition.
 The <a href="http://api.dartlang.org/dart_core/Collection.html#every">every()</a> and
 <a href="http://api.dartlang.org/dart_core/Collection.html#some">some()</a> methods
-check whether a collection matches
-every condition or at least one condition, respectively.
+check whether every item in a collection matches a condition
+or if at least one item matches a condition, respectively.
 The <a href="http://api.dartlang.org/dart_core/List.html#sort">sort()</a> method
 lets you sort a list using any criteria you like.
 </p>