Allow only applying mixins when mods aren't present

Author: embeddedt

common/src/main/java/org/embeddedt/modernfix/core/config/ModernFixEarlyConfig.java

@@ -112,7 +112,7 @@ private void scanForAndBuildMixinOptions() {
                             if(annotation.values.get(i).equals("value")) {
                                 String modId = (String)annotation.values.get(i + 1);
                                 if(modId != null) {
-                                    requiredModPresent = modPresent(modId);
+                                    requiredModPresent = modId.startsWith("!") ? !modPresent(modId.substring(1)) : modPresent(modId);
                                     requiredModId = modId;
                                 }
                                 break;