add border-spacing to default styles

Author: kernusr

src/PhpWord/Writer/HTML/Part/Head.php

@@ -101,6 +101,7 @@ private function writeStyles()
             'table' => [
                 'border' => '1px solid black',
                 'border-spacing' => '0px',
+	            'border-collapse' => 'collapse',
                 'width ' => '100%',
             ],
             'td' => [