HADOOP-19159. S3A. Fix documentation of fs.s3a.committer.abort.pending.uploads (#6778)

The description of `fs.s3a.committer.abort.pending.uploads` in the section `Concurrent Jobs writing to the same destination` is not correct. Its default value is `true`.

Contributed by Xi Chen

hadoop-tools/hadoop-aws/src/site/markdown/tools/hadoop-aws/committers.md

@@ -713,7 +713,7 @@ such use case, The "MAGIC PATH" for each job is unique of the format `__magic_jo
 multiple job running simultaneously do not step into each other.
 
 Before attempting this, the committers must be set to not delete all incomplete uploads on job commit,
-by setting `fs.s3a.committer.abort.pending.uploads` to `false`. This is set to `false`by default
+by setting `fs.s3a.committer.abort.pending.uploads` to `false`. This is set to `true` by default.
 
 ```xml
 <property>