style: fix typo (grafana#362)

docs/docs/namespaces.md

@@ -34,7 +34,7 @@ Some resources in Kubernetes are cluster-wide, meaning they don't belong to a si
 Tanka will make an attempt to not add namespaces to *known* cluster-wide types. 
 It does this with a short list of types in [the source code](https://github.com/grafana/tanka/blob/master/pkg/process/namespace.go).
 
-Tanka cannot feasably maintain this list for all known custom resource types. In those cases, resources will have namespaces added to their manifests,
+Tanka cannot feasibly maintain this list for all known custom resource types. In those cases, resources will have namespaces added to their manifests,
 and kubectl should happily apply them as non-namespaced resources.
 
 If this presents a problem for your workflow, you can **override this** behavior