[ISSUE #6982]Update the version in the README.md document to 5.1.3

[mxsm]

Which Issue(s) This PR Fixes

Fixes #6982

Brief Description

• Update the version in the README.md document to 5.1.3

How Did You Test This Change?

[codecov-commenter]

Codecov Report

Merging #6983 (1f78ce7) into develop (87075c2) will increase coverage by 0.00%.
The diff coverage is 26.02%.

@@            Coverage Diff             @@
##             develop    #6983   +/-   ##
==========================================
  Coverage      42.69%   42.70%           
- Complexity      9221     9238   +17     
==========================================
  Files           1131     1131           
  Lines          80485    80482    -3     
  Branches       10520    10515    -5     
==========================================
+ Hits           34366    34369    +3     
+ Misses         41822    41820    -2     
+ Partials        4297     4293    -4     

Impacted Files	Coverage Δ
...etmq/proxy/grpc/v2/DefaultGrpcMessingActivity.java	0.00% <0.00%> (ø)
...cketmq/proxy/grpc/v2/GrpcMessagingApplication.java	38.91% <0.00%> (ø)
...ache/rocketmq/proxy/processor/ClientProcessor.java	0.00% <ø> (ø)
...tmq/proxy/processor/DefaultMessagingProcessor.java	2.89% <0.00%> (ø)
...e/rocketmq/proxy/processor/MessagingProcessor.java	16.66% <ø> (ø)
...proxy/remoting/activity/ClientManagerActivity.java	0.00% <0.00%> (ø)
...oxy/remoting/activity/ConsumerManagerActivity.java	0.00% <0.00%> (ø)
...proxy/remoting/channel/RemotingChannelManager.java	90.69% <ø> (ø)
...q/remoting/protocol/body/LockBatchRequestBody.java	0.00% <0.00%> (ø)
...remoting/protocol/body/UnlockBatchRequestBody.java	0.00% <0.00%> (ø)
... and 8 more

... and 26 files with indirect coverage changes

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