Added ROLLBACK statement parsing.

Author: wvanbergen

lib/sql_tree/node/rollback_statement.rb

@@ -0,0 +1,12 @@
+module SQLTree::Node
+  class RollbackStatement < Base
+    def to_sql(options = {})
+      "ROLLBACK"
+    end
+
+    def self.parse(tokens)
+      tokens.consume(SQLTree::Token::ROLLBACK)
+      return self.new
+    end
+  end
+end