Invalid email input #1

[nus-pe-script]

Describe the bug
When add email without .com is still valid.

To Reproduce
Steps to reproduce the behavior:

1. Type "add John Doe p/98765432 e/johnd@gmail a/John street, block 123, Undo and redo command #1-01 s/Doctor"
2. Person is still added into the system.

Expected behavior
It should be an invalid output. Because some ends with a .sg etc

Screenshots

Additional context
NIL

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Reported by: @tristyxxnana
Severity: Medium

_{[original: nusCS2113-AY1819S1/pe-1#40]}