fix: cast automerge migration values (#924)

lib/config/migration.js

@@ -36,17 +36,17 @@ function migrateConfig(config, parentConfig) {
     } else if (key === 'automergeMinor') {
       isMigrated = true;
       migratedConfig.minor = migratedConfig.minor || {};
-      migratedConfig.minor.automerge = val;
+      migratedConfig.minor.automerge = val == true; // eslint-disable-line eqeqeq
       delete migratedConfig[key];
     } else if (key === 'automergeMajor') {
       isMigrated = true;
       migratedConfig.major = migratedConfig.major || {};
-      migratedConfig.major.automerge = val;
+      migratedConfig.major.automerge = val == true; // eslint-disable-line eqeqeq
       delete migratedConfig[key];
     } else if (key === 'automergePatch') {
       isMigrated = true;
       migratedConfig.patch = migratedConfig.patch || {};
-      migratedConfig.patch.automerge = val;
+      migratedConfig.patch.automerge = val == true; // eslint-disable-line eqeqeq
       delete migratedConfig[key];
     } else if (key === 'ignoreNodeModules') {
       isMigrated = true;