make bibtex naming convention consistent

src/casing.f90

@@ -18,7 +18,7 @@
 !>      where \f$\theta\f$ and \f$\zeta\f$ are arbitrary poloidal and toroidal angles,
 !>      and \f${\bf e}_\theta \equiv \partial {\bf x}/\partial \theta\f$, \f${\bf e}_\zeta \equiv \partial {\bf x}/\partial \zeta\f$.
 !>      This routine assumes that the plasma boundary is a flux surface, i.e. \f${\bf B} \cdot {\bf e}_\theta \times {\bf e}_\zeta = 0\f$. </li>
-!> <li> The virtual casing principle (Shafranov & Zakharov (1972) \cite y1972_shafranov_zakharov, Lazerson (2012) \cite y2012_lazerson and Hanson (2015) \cite y2015_hanson)
+!> <li> The virtual casing principle (Shafranov & Zakharov (1972) \cite y1972_shafranov, Lazerson (2012) \cite y2012_lazerson and Hanson (2015) \cite y2015_hanson)
 !>      shows that the field outside/inside the plasma arising from plasma currents inside/outside the boundary
 !>      is equivalent to the field generated by a surface current,
 !>      \f{eqnarray}{ {\bf j} = {\bf B}_s \times {\bf n},