minor fixes

activesupport/lib/active_support/core_ext/string/behavior.rb

@@ -1,6 +1,5 @@
 class String
-  # Enable more predictable duck-typing on String-like classes. See
-  # Object#acts_like?.
+  # Enable more predictable duck-typing on String-like classes. See <tt>Object#acts_like?</tt>.
   def acts_like_string?
     true
   end

activesupport/lib/active_support/core_ext/string/exclude.rb

@@ -1,5 +1,5 @@
 class String
-  # The inverse of String#include?. Returns true if the string does not include the other string.
+  # The inverse of <tt>String#include?</tt>. Returns true if the string does not include the other string.
   def exclude?(string)
     !include?(string)
   end

activesupport/lib/active_support/core_ext/string/inquiry.rb

@@ -1,7 +1,7 @@
 require 'active_support/string_inquirer'
 
 class String
-  # Wraps the current string in the ActiveSupport::StringInquirer class,
+  # Wraps the current string in the <tt>ActiveSupport::StringInquirer</tt> class,
   # which gives you a prettier way to test for equality. Example:
   #
   #   env = "production".inquiry