Pin Milvus to <2.0.0

[ZanSara]

Due to the new 2.0.0 release, we should pin pymilvus<2.0.0 for now

[julian-risch]

LGTM. Let's create another issue though to make sure haystack also works with pymilvus 2.0 (and beyond in future). The comment here on
# For milvus 2.x version use this library 'pymilvus===2.0.0rc6' can also be removed then.

[ZanSara]

The incoming PR on dependency management (#1994) actually takes care of this Milvus breaking change: there are two different dependency groups for both versions. Do you think I should change the default to Milvus2? Our integration with it not yet very well tested, but on the other hand if we never use it we'll never know if it works 😄

[julian-risch]

if haystack works with 2.0 thanks to the upcoming #1994 PR, I would be happy to have 2.0 as the default, yes. Knowing whether it works or not that's what our test cases are for ;)

[ZanSara]

Cool, then let's leave this one as it is as a quick patch. I believe #1994 could be merged tomorrow or after-tomorrow at most.

[HAIXteam]

Hello, We are having an issue with pymilvus. please advise any help on this?

1)we installled farm-haystack==0.9.0
2) We installed pip3 install pymilvus==1.1.2

File "/app/main.py", line 6, in
from haystack import document_store
File "/usr/local/lib/python3.7/site-packages/haystack/init.py", line 5, in
from haystack.finder import Finder
File "/usr/local/lib/python3.7/site-packages/haystack/finder.py", line 8, in
from haystack.reader.base import BaseReader
File "/usr/local/lib/python3.7/site-packages/haystack/reader/init.py", line 1, in
from haystack.reader.farm import FARMReader
File "/usr/local/lib/python3.7/site-packages/haystack/reader/farm.py", line 21, in
from haystack.document_store.base import BaseDocumentStore
File "/usr/local/lib/python3.7/site-packages/haystack/document_store/init.py", line 4, in
from haystack.document_store.milvus import MilvusDocumentStore
File "/usr/local/lib/python3.7/site-packages/haystack/document_store/milvus.py", line 7, in
from milvus import IndexType, MetricType, Milvus, Status
ModuleNotFoundError: No module named 'milvus'