Fix prop-types to check for computed prop names.

[burnnat]

Previously, accessing props dynamically with an expression like this.props[propName] would result in a linting error like:

'propName' is missing in props validation

However "propName" is simply the name of a variable, not the actual property name. Since there's no easy way to resolve the real property name for dynamic accesses like this, this modification simply ignores such cases.

[coveralls]

Coverage remained the same at 96.73% when pulling 3b5cf97 on burnnat:computed-prop-types into 0d7b069 on yannickcr:master.

[burnnat]

Looks like the Travis failure is unrelated to the code change - seems to be a connection issue, maybe because of the Github DDOS.

[yannickcr]

Merged, thanks.