[GOBBLIN-1611] Fix a wrong value for writer.codec.type in the document

[sekikn]

Dear Gobblin maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• [x] My PR addresses the following Gobblin JIRA issues and references them in the PR title. For example, "[GOBBLIN-XXX] My Gobblin PR"
  • https://issues.apache.org/jira/browse/GOBBLIN-1611

Description

• [x] Here are some details about my PR, including screenshots (if applicable):

The description about the writer.codec.type property in the document has a little mistake. This PR corrects it.

Tests

• [x] My PR adds the following unit tests OR does not need testing for this extremely good reason:

No additional test, since it's just a documentation fix. I ran mkdocs serve locally and confirmed the document was modified as expected.

Commits

• [x] My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

[codecov-commenter]

Codecov Report

Merging #3470 (dc04999) into master (655826a) will increase coverage by 0.00%. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #3470   +/-   ##
=========================================
  Coverage     46.62%   46.62%           
+ Complexity    10352    10351    -1     
=========================================
  Files          2076     2076           
  Lines         81032    81032           
  Branches       9044     9044           
=========================================
+ Hits          37778    37781    +3     
+ Misses        39774    39772    -2     
+ Partials       3480     3479    -1     

Impacted Files	Coverage Δ
...gobblin/service/modules/core/GitConfigMonitor.java	81.35% <0.00%> (-1.70%)	:arrow_down:
...anagement/copy/replication/ConfigBasedDataset.java	68.87% <0.00%> (ø)
.../apache/gobblin/runtime/api/JobExecutionState.java	80.37% <0.00%> (+0.93%)	:arrow_up:
...lin/util/filesystem/FileSystemInstrumentation.java	92.85% <0.00%> (+7.14%)	:arrow_up:
...he/gobblin/source/PartitionAwareFileRetriever.java	55.55% <0.00%> (+7.40%)	:arrow_up:

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[Will-Lo]

Thanks for the contribution! @sekikn