I think you ran into a php quote problem, you can fix but im no expert in nesting php quotes
you could try escape all your double quotes like
$config['alert']['macros']['rule']['vendor_juniper'] = 'devices.os LIKE \"%junos%\" AND
(devices.sysObjectID LIKE \".1.3.6.1.4.1.2636.%\" OR devices.sysObjectID LIKE
\".1.3.6.1.4.1.12532.%\")';
Alternatively did you look at using Override SQL alert instead of a MACRO ?
e.g Threshold for traffic alertings