fix: print valid flag values in error message when using exactlyOne

[cristiand391]

When a flag uses the exactlyOne flag property in one command and then you run the command without passing any flag you get a wrong error message.

ERROR running command:test:  Exactly one of the following must be provided: m,a,n,i,f,e,s,t

With this fix:

ERROR running command:test:  Exactly one of the following must be provided: --manifest, --metadata, --sourcepath, --validateddeployrequestid

[salesforce-cla]

Thanks for the contribution! It looks like @cristiand391 is an internal user so signing the CLA is not required. However, we need to confirm this.

[salesforce-cla]

Thanks for the contribution! It looks like @cristiand391 is an internal user so signing the CLA is not required. However, we need to confirm this.