Rename database client classes

Update our class names to reflect the new file structure introduced in
b700c1bef89a67a64f1040fb6bb03c0320eefe91.

Use the

    module DBShell
      module Client
      end
    end

syntax intead of `DBShell::Client` so that we don't have to define the
`Client` module in a separate file and require it. Otherwise we'd get an
error:

    lib/dbshell/client/sqlite3.rb:1:in `<top (required)>': uninitialized constant DBShell::Client (NameError)

1 files changed, 2 insertions, 2 deletions

diff --git a/spec/dbshell/client/sqlite3_spec.rb b/spec/dbshell/client/sqlite3_spec.rb
index df42cbd..15d35a5 100644
--- a/spec/dbshell/client/sqlite3_spec.rb
+++ b/spec/dbshell/client/sqlite3_spec.rb
@@ -1,10 +1,10 @@
 require 'minitest/autorun'
 require 'dbshell/client/sqlite3'
 
-describe DBShell::Sqlite3Client do
+describe DBShell::Client::Sqlite3 do
   describe ".build_command" do
     it "builds basic arguments" do
-      DBShell::Sqlite3Client.build_command({
+      DBShell::Client::Sqlite3.build_command({
         'adapter' => 'sqlite3',
         'database' => 'db/development.sqlite3'
       }).must_equal([