message: Fix: `purser-software` common wallet interface docs link
diff: A `javascript` library to interact with a software Ethereum wallet, based on the [ethers.js](https://github.com/ethers-io/ethers.js/) library.
  -It extracts all the complexity from setting up, maintaining and interacting with it, while providing you with a [predictable interface](https://docs.colony.io/purser/api-wallet-object/).
  +It extracts all the complexity from setting up, maintaining and interacting with it, while providing you with a [predictable interface](https://docs.colony.io/purser/interface-common-wallet-interface/).
  ### Installation
  ```js
  