Guard against word splitting due to spaces

Author: desrosj

.env.default

@@ -33,10 +33,10 @@ export WPT_DB_PASSWORD=""
 export WPT_DB_HOST=""
 
 # (Optionally) set a custom table prefix to permit concurrency against the same database.
-export WPT_TABLE_PREFIX=${WPT_TABLE_PREFIX-wptests_}
+export WPT_TABLE_PREFIX="${WPT_TABLE_PREFIX-wptests_}"
 
 # (Optionally) define the PHP executable to be called
-export WPT_PHP_EXECUTABLE=${WPT_PHP_EXECUTABLE-php}
+export WPT_PHP_EXECUTABLE="${WPT_PHP_EXECUTABLE-php}"
 
 # (Optionally) define the PHPUnit command execution call.
 # Use if `php phpunit.phar` can't be called directly for some reason.