fix: set isDevHub when --setdefaultdevhubusername is passed (#375)

Author: WillieRuemmele

src/common.ts

@@ -23,6 +23,9 @@ export class Common {
     if (flags.setalias) await authInfo.setAlias(flags.setalias);
 
     if (flags.setdefaultdevhubusername || flags.setdefaultusername) {
+      if (flags.setdefaultdevhubusername) {
+        await authInfo.save({ isDevHub: true });
+      }
       await authInfo.setAsDefault({
         defaultUsername: flags.setdefaultusername,
         defaultDevhubUsername: flags.setdefaultdevhubusername,