`hasOwnProperty(number)` can return true for strings.
This is unlikely to be the desired usage, and can mean that odd
responses are returned by nconf.
Disable trying to check `hasOwnProperty` of strings.
Previously, if the Memory store was merged with an object containing a null value, the following Error occurred:
TypeError: Object.keys called on non-object
at Function.keys (native)
at Memory.merge (/.../node_modules/nconf/lib/nconf/stores/memory.js:199:17)
at Memory.merge (/.../node_modules/nconf/lib/nconf/stores/memory.js:200:17)
at Array.every (native)
at Memory.merge (/.../node_modules/nconf/lib/nconf/stores/memory.js:199:29)
at common.merge (/.../node_modules/nconf/lib/nconf/common.js:99:13)
at Array.forEach (native)
at common.merge (/.../node_modules/nconf/lib/nconf/common.js:98:22)
at Array.forEach (native)
at Object.common.merge (/.../node_modules/nconf/lib/nconf/common.js:97:8)
This commit prevents that.