Modify `deprecate` debug helper to handle single arg.

[rwjblue]

This should not throw (though Ember will issue a deprecation for not passing the options hash):

import { deprecate } from '@ember/debug';

deprecate('some message');

Currently the following (lovely) error is thrown:

TypeError: -private/system/store.js: Property expression of ParenthesizedExpression expected node to be of a type ["Expression"] but instead got null
    at Object.validate (/Users/rjackson/src/open-source/ember-data/node_modules/babel-types/lib/definitions/index.js:109:13)
    at validate (/Users/rjackson/src/open-source/ember-data/node_modules/babel-types/lib/index.js:505:9)
    at Object.builder (/Users/rjackson/src/open-source/ember-data/node_modules/babel-types/lib/index.js:466:7)
    at Builder.deprecate (/Users/rjackson/src/open-source/ember-data/node_modules/babel-plugin-debug-macros/dist/lib/utils/builder.js:187:92)
    at Macros.build (/Users/rjackson/src/open-source/ember-data/node_modules/babel-plugin-debug-macros/dist/lib/utils/macros.js:189:36)
    at PluginPass.ExpressionStatement (/Users/rjackson/src/open-source/ember-data/node_modules/babel-plugin-debug-macros/dist/index.js:67:27)
    at newFn (/Users/rjackson/src/open-source/ember-data/node_modules/babel-traverse/lib/visitors.js:276:21)
    at NodePath._call (/Users/rjackson/src/open-source/ember-data/node_modules/babel-traverse/lib/path/context.js:76:18)
    at NodePath.call (/Users/rjackson/src/open-source/ember-data/node_modules/babel-traverse/lib/path/context.js:48:17)
    at NodePath.visit (/Users/rjackson/src/open-source/ember-data/node_modules/babel-traverse/lib/path/context.js:105:12)