set core at 0.18

Author: tolecar

composer.json

@@ -11,7 +11,7 @@
 		"php" : "^7.2",
 		"psr/log" : "^1.1.0",
 		"psr/simple-cache" : "^1.0.1",
-		"zef-dev/convoworks-core" : "^1.0.0"
+		"zef-dev/convoworks-core" : "^0.18"
 	},
 	"autoload" : {
 		"psr-4" : {