Fix bug with printing pinned dependencies.

Brew prints this error:
```
Error: undefined method `join' for nil:NilClass
```

because, in this code:

```ruby
puts pinned_dependents.map do |f|
  "#{f.full_specified_name} #{f.pkg_version}"
end.join(", ")
```
the block is passed to `puts` and not to `map`. `.join(",")` is called on the output of `puts`.

(I think the regression was introduced in this commit: e12a7b08)

Library/Homebrew/cmd/upgrade.rb

@@ -239,9 +239,9 @@ module Homebrew
     if pinned_dependents.present?
       plural = "dependent".pluralize(pinned_dependents.count)
       ohai "Not upgrading #{pinned_dependents.count} pinned #{plural}:"
-      puts pinned_dependents.map do |f|
+      puts(pinned_dependents.map do |f|
         "#{f.full_specified_name} #{f.pkg_version}"
-      end.join(", ")
+      end.join(", "))
     end
 
     # Print the upgradable dependents.
@@ -292,9 +292,9 @@ module Homebrew
       count = pinned_broken_dependents.count
       plural = "dependent".pluralize(pinned_broken_dependents.count)
       onoe "Not reinstalling #{count} broken and outdated, but pinned #{plural}:"
-      $stderr.puts pinned_broken_dependents.map do |f|
+      $stderr.puts(pinned_broken_dependents.map do |f|
         "#{f.full_specified_name} #{f.pkg_version}"
-      end.join(", ")
+      end.join(", "))
     end
 
     # Print the broken dependents.