doc: Fix typo in docs

PR-URL: #285
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Nicola Del Gobbo <nicoladelgobbo@NickNaso.local>

doc/promises.md

@@ -1,4 +1,4 @@
-You are reading a draft of the next documentation and it's in continuos update so
+You are reading a draft of the next documentation and it's in continuous update so
 if you don't find what you need please refer to:
 [C++ wrapper classes for the ABI-stable C APIs for Node.js](https://nodejs.github.io/node-addon-api/)