Merge pull request #4151 from rsalmond/typofix

small typo fix

docs/securing_installation.md

@@ -34,7 +34,7 @@ There are four main areas to consider when securing a tiller installation:
 
 ### RBAC
 
-Recent versions of Kubernetes employ a [role-based access control (or RBAC)](https://en.wikipedia.org/wiki/Role-based_access_control) system (as do modern operating systems) to help mitigate the damage that can done if credentials are misused or bugs exist. Even where an identity is hijacked, the identity has only so many permissions to a controlled space. This effectively adds a layer of security to limit the scope of any attack with that identity. 
+Recent versions of Kubernetes employ a [role-based access control (or RBAC)](https://en.wikipedia.org/wiki/Role-based_access_control) system (as do modern operating systems) to help mitigate the damage that can be done if credentials are misused or bugs exist. Even where an identity is hijacked, the identity has only so many permissions to a controlled space. This effectively adds a layer of security to limit the scope of any attack with that identity.
 
 Helm and Tiller are designed to install, remove, and modify logical applications that can contain many services interacting together. As a result, often its usefulness involves cluster-wide operations, which in a multitenant cluster means that great care must be taken with access to a cluster-wide Tiller installation to prevent improper activity.