fix typo in unsupported/NumericalDiff

unsupported/Eigen/src/NumericalDiff/NumericalDiff.h

diff --git a/unsupported/Eigen/src/NumericalDiff/NumericalDiff.h b/unsupported/Eigen/src/NumericalDiff/NumericalDiff.h
index 36df9f5..8651585 100644
--- a/unsupported/Eigen/src/NumericalDiff/NumericalDiff.h
+++ b/unsupported/Eigen/src/NumericalDiff/NumericalDiff.h
@@ -66,7 +66,7 @@
     template<typename T0, typename T1>
         NumericalDiff(const T0& a0, const T1& a1) : Functor(a0, a1), epsfcn(0) {}
     template<typename T0, typename T1, typename T2>
-        NumericalDiff(const T0& a0, const T1& a1, const T1& a2) : Functor(a0, a1, a2), epsfcn(0) {}
+        NumericalDiff(const T0& a0, const T1& a1, const T2& a2) : Functor(a0, a1, a2), epsfcn(0) {}
 
     enum {
         InputsAtCompileTime = Functor::InputsAtCompileTime,