Fix `var_export` return in `WP_CLI::print_value`
Fix `var_export` return in `WP_CLI::print_value`

By default `var_export` will dump its output to stdout. Set the return
parameter to true to save it into the `$value` variable for further
processing as expected.

aaemnnosttv/wp-cli,aaemnnosttv/wp-cli,rodrigoprimo/wp-cli,trepmal/wp-cli,rodrigoprimo/wp-cli,trepmal/wp-cli,rodrigoprimo/wp-cli,aaemnnosttv/wp-cli,trepmal/wp-cli