Fix phpdocs for fluent interfaces.

Backported from a092f6d (master).

[ci skip]

lib/Predis/Pipeline/PipelineContext.php

@@ -65,9 +65,9 @@ class PipelineContext implements BasicClientInterface, ExecutableContextInterfac
     /**
      * Queues a command into the pipeline buffer.
      *
-     * @param  string          $method    Command ID.
-     * @param  array           $arguments Arguments for the command.
-     * @return PipelineContext
+     * @param  string $method    Command ID.
+     * @param  array  $arguments Arguments for the command.
+     * @return $this
      */
     public function __call($method, $arguments)
     {

lib/Predis/Transaction/MultiExecContext.php

@@ -200,8 +200,8 @@ class MultiExecContext implements BasicClientInterface, ExecutableContextInterfa
     /**
      * Executes the specified Redis command.
      *
-     * @param  CommandInterface $command A Redis command.
-     * @return mixed
+     * @param  CommandInterface $command Command instance.
+     * @return $this|mixed
      */
     public function executeCommand(CommandInterface $command)
     {