Grabbing is failing since 24th January

SGL_GrabVariable grab data from SGL web site and returns a dataframe with 2 columns:

• datetime unix timestamp format
• `value the value of the data

It seems that the format of the timestamp has changed on the SGL website:

> varlist <- SGL_GrabVariableListLake("https://seinegrandslacs.fr/quatre-lacs-reservoirs/lac-reservoir-seine")
> SGL_GrabVariable(varlist$link[1])
datetime value           
0  2021-03-15T08:00    18
1  2021-03-14T08:00    18
2  2021-03-13T08:00    15
3  2021-03-12T08:00    15
4  2021-03-11T08:00    15
5  2021-03-10T08:00    15
6  2021-03-09T08:00    16
7  2021-03-08T08:00    20
8  2021-03-07T08:00    21
9  2021-03-06T08:00    19
10 2021-03-05T08:00    25