Better handling for bidModifier in examples

[dklimkin]

Logging based on:

https://groups.google.com/forum/#!msg/adwords-api/pOxbk6fzZMU/Ltd9Ote_pywJ

$value = 'none';
if (!empty($modifier->bidModifier)) {
   $value = $modifier->bidModifier;
}

There should be used is_numeric instead of !empty, since 0.0 looks like empty, but it's actually -100%, and that should be treated as well.

[vtsao]

This will be fixed in the next release. Will ping here when it's out.

[vtsao]

Fixed in 6.7.0 release.