FT: fix example

src/gridtools/FourierTransform.cpp

@@ -59,7 +59,7 @@ The default values of these parameters are: \f$a=1\f$ and \f$b=1\f$.
 The following example tells Plumed to compute the complex 2D 'backward' Discrete Fourier Transform by taking the data saved on a grid called 'density', and normalizing the output by \f$ \frac{1}{\sqrt{N_x\, N_y}}\f$, where \f$N_x\f$ and \f$N_y\f$ are the number of data on the grid (it can be the case that \f$N_x\neq N_y\f$):
 
 \plumedfile
-FOURIER_TRANSFORM STRIDE=1 GRID=density FT_TYPE=complex FOURIER_PARAMETERS=0,-1 FILE=fourier.dat
+FOURIER_TRANSFORM STRIDE=1 GRID=density FT_TYPE=complex FOURIER_PARAMETERS=0,-1 
 \endplumedfile
 
 */