stack/erp5: fix pandas version in erp5

The version of pandas was overwritten in
02fad6a8 but didn't work with python2.

Then the version was downgraded to 0.24.2 in
15569ea9 but ERP5 doesn't work with this
pandas version:
Traceback (most recent call last):
  File "/srv/slapgrid/slappart3/t/dgg/soft/63c49071f5be63057dd48d7a85c10226/bin/runTestSuite", line 325, in <module>
    import Products.ERP5Type.tests.runTestSuite
  File "/srv/slapgrid/slappart3/t/dgg/soft/63c49071f5be63057dd48d7a85c10226/parts/erp5/product/ERP5Type/__init__.py", line 92, in <module>
    from . import ZopePatch
  File "/srv/slapgrid/slappart3/t/dgg/soft/63c49071f5be63057dd48d7a85c10226/parts/erp5/product/ERP5Type/ZopePatch.py", line 30, in <module>
    from Products.ERP5Type.patches import Restricted
  File "/srv/slapgrid/slappart3/t/dgg/soft/63c49071f5be63057dd48d7a85c10226/parts/erp5/product/ERP5Type/patches/Restricted.py", line 491, in <module>
    allow_type(pd.indexes.range.RangeIndex)
AttributeError: 'module' object has no attribute 'indexes'

So reuse old version 0.19.2

stack/erp5/buildout.cfg

@@ -865,3 +865,4 @@ strict-rfc3339 = 0.7
 webcolors = 1.10
 rfc3987 = 1.3.8
 jsonpointer = 2.2
+pandas = 0.19.2