function TokenCredential (token) {
  this.token = token;
}
Creates a new TokenCredential object.
@class
The TokenCredential class is used to store the access token string.

@constructor
@param {string} token The access token, such as an OAuth access token in string type.

@example
var azure = require('azure-storage');
var tokenCredential = new azure.TokenCredential('myOAuthAccessToken');
var blobService = azure.createBlobServiceWithTokenCredential('https://account.blob.core.windows.net', tokenCredential);
tokenCredential.set('updatedOAuthAccessToken');