Update COA version to avoid conflict

````
npm WARN unmet dependency /Users/tadatuta/Sites/project-stub/node_modules/bem/node_modules/apw requires coa@'~0.4.0' but will load
npm WARN unmet dependency /Users/tadatuta/Sites/project-stub/node_modules/bem/node_modules/coa,
npm WARN unmet dependency which is version 0.3.9
````