Fix cannot read response data included terminator when use meta protocol

[matsubara0507]

if meta protocol get response data included terminator \r\n then occur error

  1) Error:
operations::using the meta protocol::get#test_0002_return the value that include TERMINATOR on a hit:
Dalli::UnmarshalError: Unable to unmarshal value: marshal data too short
    lib/dalli/protocol/value_serializer.rb:65:in `filter_argument_error'
    lib/dalli/protocol/value_serializer.rb:51:in `rescue in retrieve'
    lib/dalli/protocol/value_serializer.rb:45:in `retrieve'
    lib/dalli/protocol/value_marshaller.rb:44:in `retrieve'
    lib/dalli/protocol/meta/response_processor.rb:35:in `meta_get_with_value'
    lib/dalli/protocol/meta.rb:30:in `get'
    lib/dalli/protocol/base.rb:36:in `request'
    lib/dalli/options.rb:18:in `block in request'
    lib/dalli/options.rb:17:in `synchronize'
    lib/dalli/options.rb:17:in `request'
    lib/dalli/client.rb:426:in `perform'
    lib/dalli/client.rb:64:in `get'
    test/integration/test_operations.rb:32:in `block (6 levels) in <top (required)>'
    test/helpers/memcached.rb:41:in `memcached'
    test/helpers/memcached.rb:50:in `memcached_persistent'
    test/integration/test_operations.rb:27:in `block (5 levels) in <top (required)>'

Meta get response include size of data block.
ref. https://github.com/memcached/memcached/blob/1.6.29/doc/protocol.txt#L519

Therefore, changed to read response data using size instead of terminator.