Fail to write gofr to stat.h5

Dear Developers,

I used nexus to generate inputs for estimators, following examples in https://github.com/QMCPACK/qmcpack/tree/develop/nexus/examples/qmcpack/rsqmc_misc/estimators, and I failed to output gofr. The error message is: **Fatal Error. Aborting at EstimatorManager input:unparsable node, name: gofr type: gofr in Estimators input.**

My nexus setting is:

```
from qmcpack_input import spindensity
sdens = spindensity(
grid = (120,120,120),
)

from qmcpack_input import gofr
gofr = gofr(type='gofr',
name='gofr',
num_bin = 1000,
rmax = 10,
)

qmc = generate_qmcpack(
identifier = 'dmc',
path = 'silicon_est2/twist_conv/n' + str(nk),
job = job(nodes=4,
threads=1,
hours=1,
app=qmc_bin),
input_type = 'basic',
system = supercell,
pseudos = ['Si.ccECP.xml'],
estimators = [sdens,gofr],
qmc = 'dmc',

# Initial VMC stuff
vmc_warmupsteps = 8, # Number of Equilibration steps
vmc_blocks = 200, # Number of VMC blocks (To generate the DMC samples)
vmc_steps = 1, # Number of VMC steps (To generate DMC samples)
vmc_timestep = 0.1, # VMC Timestep (To Generate DMC samples)

# DMC stuff
timestep = 0.01, # DMC timestep
steps = 1, # start with small number for large timesteps [autocorrelation]
blocks = 300, # Number of DMC blocks
total_walkers = 512,
dependencies = [(convk,'orbitals'),
(optJ12,'jastrow')],
)
```

This nexus setting gives me the setting for the estimators as follows:
```

...




120 120 120






...

```

I think this problem comes from qmcpack cannot recognize gofr which defined in QMCHamiltonians. If I only request spin density, everything is fine.

Thank you.