Spirit Airlines Inc tanked 20% in premarket on Monday after JetBlue Airways Corporation terminated its $3.8 billion merger agreement with the ultra-low-cost carrier.The news arrives shortly after a federal judge blocked $JBLU from buying Spirit Airlines – citing the deal could increase fares for price-sensitive travellers. JetBlue and $SAVE had together appealed that ruling in line with terms of the planned transaction. Joanna Geraghty – chief executive of JetBlue said today:“We were right to compete with F ...