fix typo in doc for ParametrizedLine

Eigen/src/Geometry/ParametrizedLine.h

@@ -34,7 +34,7 @@
   *
   * A parametrized line is defined by an origin point \f$ \mathbf{o} \f$ and a unit
   * direction vector \f$ \mathbf{d} \f$ such that the line corresponds to
-  * the set \f$ l(t) = \mathbf{o} + t \mathbf{d} \f$, \f$ l \in \mathbf{R} \f$.
+  * the set \f$ l(t) = \mathbf{o} + t \mathbf{d} \f$, \f$ t \in \mathbf{R} \f$.
   *
   * \param _Scalar the scalar type, i.e., the type of the coefficients
   * \param _AmbientDim the dimension of the ambient space, can be a compile time value or Dynamic.