message: tweaking examples
diff: @@ -203,7 +203,7 @@ This call will return the USD value for the specified amount of the specified to
  ```js
  let exchangeRate = new ExchangeRate(web3);
  -let usdPrice = await exchangeRate.getUSDPrice(token, amountInWei);
  +let usdPrice = await exchangeRate.getUSDPrice("DAI", amountInWei);
  console.log(`USD value: $${usdPrice.toFixed(2)} USD`);
  ```
  ### `ExchangeRate.getETHPrice`
  @@ -211,7 +211,7 @@ This call will return the ETH value for the specified amount of the specified to
  ```js
  let exchangeRate = new ExchangeRate(web3);
  -let ethWeiPrice = await exchangeRate.getETHPrice(token, amountInWei);
  +let ethWeiPrice = await exchangeRate.getETHPrice("CARD", amountInWei);
  console.log(`ETH value: ${fromWei(ethWeiPrice)} ETH`);
  ```
  ### `ExchangeRate.getUpdatedAt`
  @@ -219,7 +219,7 @@ This call will return a `Date` instance that indicates the date the token rate w
  ```js
  let exchangeRate = new ExchangeRate(web3);
  -let date = await exchangeRate.getUpdatedAt(token);
  +let date = await exchangeRate.getUpdatedAt("DAI");
  console.log(`The ${token} rate was last updated at ${date.toString()}`);
  ```
  ## `getAddress`
  