[Update] Allow specifying root names

Closes https://github.com/CocoaPods/CocoaPods/issues/3689.

CHANGELOG.md

@@ -83,6 +83,11 @@ To install release candidates run `[sudo] gem install cocoapods --pre`
   [Hugo Tunius](https://github.com/k0nserv)
   [#995](https://github.com/CocoaPods/CocoaPods/issues/995)
 
+* `pod update` will now accept root pod names, even when only subspecs are
+  installed.  
+  [Samuel Giddins](https://github.com/segiddins)
+  [#3689](https://github.com/CocoaPods/CocoaPods/issues/3689)
+
 ##### Bug Fixes
 
 * Added recursive support to the public headers of vendored frameworks

lib/cocoapods/command/project.rb

@@ -134,8 +134,9 @@ module Pod
           verify_lockfile_exists!
 
           # Check if all given pods are installed
-          missing_pods = @pods.select do |pod|
-            !config.lockfile.pod_names.include?(pod)
+          lockfile_roots = config.lockfile.pod_names.map { |p| Specification.root_name(p) }
+          missing_pods = @pods.map { |p| Specification.root_name(p) }.select do |pod|
+            !lockfile_roots.include?(pod)
           end
 
           if missing_pods.length > 0