Extended email regexp to take a 6 character TLD

TLD's currently also include 6 letter names, such as  .museum and .travel
(e.g. allabout.travel is a current website). 

This fix allows the REGEX to parse these successfully.  It does not take into account internationalised TLD's (such as Hong Kong's "公司.香港" TLD), but this is outside the scope of this little fix!