Make it strong mode clean.

CHANGELOG.md

+## 0.13.3+5
+
+* Make strong mode clean.
+
 ## 0.13.3+4
 
 * Use the proper `usage` getter in the README.
 
 ## 0.13.3+3
 
 * Add an explicit default value for the `allowTrailingOptions` parameter to `new
   ArgParser()`. This doesn't change the behavior at all; the option already
   defaulted to `false`, and passing in `null` still works.
 
@@ skipping 69 matching lines @@
 * Widen the version constraint on the `collection` package.
 
 ## 0.12.0+1
 
 * Remove the documentation link from the pubspec so this is linked to
   pub.dartlang.org by default.
 
 ## 0.12.0
 
 * Removed public constructors for `ArgResults` and `Option`.
- 
+
 * `ArgResults.wasParsed()` can be used to determine if an option was actually
   parsed or the default value is being returned.
 
 * Replaced `isFlag` and `allowMultiple` fields in the `Option` class with a
   three-value `OptionType` enum.
-  
+
 * Options may define `valueHelp` which will then be shown in the usage.
 
 ## 0.11.0
 
 * Move handling trailing options from `ArgParser.parse()` into `ArgParser`
   itself. This lets subcommands have different behavior for how they handle
   trailing options.
 
 ## 0.10.0+2
 
 * Usage ignores hidden options when determining column widths.