BERLIN (Reuters) – The value of online exports in six of the top e-commerce markets will grow fivefold to $130 billion by 2020, with Britain currently generating the biggest online trade surplus by selling more goods abroad, research showed on Monday. The study by London-based management consultancy OCC and U.S. search engine Google estimated the value of cross-border online trade in the United States, Britain, Germany, the Nordics, the Netherlands and France at $25 billion for 2013. …