Catch path alias scaling (#1057)

* Catch path alias scaling

* Better wording

* Fix grammar mistake

errors/scaling-path-alias.md

@@ -0,0 +1,12 @@
+# Scaling path alias
+
+#### Why This Error Occurred
+
+You tried to use `now scale` on a path alias (`now alias -r rules.json`). 
+
+#### Possible Ways to Fix It
+
+Path aliases are routes to instances. Instances can be scaled independent from each other.
+You can view path aliases by running `now alias ls <id>`.
+
+Documentation for Path Aliases can be found [here](https://zeit.co/docs/features/path-aliases).

src/providers/sh/commands/scale.js

@@ -195,6 +195,13 @@ async function run({ token, sh: { currentTeam } }) {
       console.error(error(`Could not find any deployments matching ${id}`))
       return process.exit(1)
     }
+
+    // Alias is a path alias, these can't be scaled.
+    if(aliasDeployment.rules && aliasDeployment.rules.length > 0) {
+      console.error(error(`Requested identifier is a path alias. https://err.sh/now-cli/scaling-path-alias`))
+      return process.exit(1)
+    }
+    
     match = deployments.find(d => {
       return d.uid === aliasDeployment.deploymentId
     })