Writing dataframe error
**Describe the bug**
Revtrieving values from TM1 and writing back ignores decimal. Values in cube are now much higher. Dataframe values are with correct decimal. 

Probably something to do with the language setup. Local machine ENG, Server GER. 

**To Reproduce**
```Python

cubeName = "plan_BudgetPlan"

from mdxpy import *
mdx = MdxBuilder.from_cube(cubeName) \\
.add_hierarchy_set_to_axis(1, MdxHierarchySet.all_leaves("plan_version")) \\
.add_hierarchy_set_to_axis(1, MdxHierarchySet.all_leaves("plan_business_unit")) \\
.add_hierarchy_set_to_axis(1, MdxHierarchySet.all_leaves("plan_department")) \\
.add_hierarchy_set_to_axis(1, MdxHierarchySet.all_leaves("plan_chart_of_accounts")) \\
.add_hierarchy_set_to_axis(1, MdxHierarchySet.member(Member.of("plan_exchange_rates",'local'))) \\
.add_hierarchy_set_to_axis(1, MdxHierarchySet.member(Member.of("plan_source",'input'))) \\
.add_hierarchy_set_to_axis(0, MdxHierarchySet.all_leaves("plan_time")) \\
.to_mdx()

with TM1Service(address=servername, port=instanceport, ssl=True, integrated_login=True, integrated_login_host=spn) as tm1:
      df = tm1.cubes.cells.execute_mdx_dataframe(mdx)

print(df.head(10))

with TM1Service(address=servername, port=instanceport, ssl=True, integrated_login=True, integrated_login_host=spn) as tm1:
  tm1.cells.write_dataframe(cubeName, df)
```

**Expected behavior**
A clear and concise description of what you expected to happen.

**Version**
TM1py Current GitHub Master
TM1 Server Version: 2.0.9.3

diff --git a/TM1py/Services/CellService.py b/TM1py/Services/CellService.py
index 2ce425f..9ad3cf4 100644
--- a/TM1py/Services/CellService.py
+++ b/TM1py/Services/CellService.py
@@ -526,7 +526,7 @@ class CellService(ObjectService):
                     dim, dim, elem)
                 for dim, elem
                 in zip(dimensions, element_tuple)]
-            body_as_dict["Value"] = str(value) if value else ""
+            body_as_dict["Value"] = value if value else ""
             updates.append(json.dumps(body_as_dict, ensure_ascii=False))
         updates = '[' + ','.join(updates) + ']'
         return self._rest.POST(url=url, data=updates, **kwargs)
['TM1py/Services/CellService.py']