[snmpd]: Fix typo in is_platform_arista (#1634)

Author: yurypm

dockers/docker-snmp-sv2/snmpd-config-updater

@@ -238,7 +238,7 @@ def is_platform_arista():
 
     if proc.returncode != 0:
         log_error("Failed to retrieve platform string")
-        return false
+        return False
 
     return "arista" in stdout