fixed misspelled word (#3816)

fixed spelled of installd to installed

README.md

@@ -116,7 +116,7 @@ prebid.requestBids({
 
 *Note:* In the 1.24.0 release of Prebid.js we have transitioned to using gulp 4.0 from using gulp 3.9.1.  To compily with gulp's recommended setup for 4.0, you'll need to have `gulp-cli` installed globally prior to running the general `npm install`.  This shouldn't impact any other projects you may work on that use an earlier version of gulp in it's setup.
 
-If you have a previous version of `gulp` installed globally, you'll need to remove it before installing `gulp-cli`.  You can check if this is installed by running `gulp -v` and seeing the version that's listed in the `CLI` field of the output.  If you have the `gulp` package installd globally, it's likely the same version that you'll see in the `Local` field.  If you already have `gulp-cli` installed, it should be a lower major version (it's at version `2.0.1` at the time of the transition).
+If you have a previous version of `gulp` installed globally, you'll need to remove it before installing `gulp-cli`.  You can check if this is installed by running `gulp -v` and seeing the version that's listed in the `CLI` field of the output.  If you have the `gulp` package installed globally, it's likely the same version that you'll see in the `Local` field.  If you already have `gulp-cli` installed, it should be a lower major version (it's at version `2.0.1` at the time of the transition).
 
 To remove the old package, you can use the command: `npm rm gulp -g`