[Java] Typo in the document

[asfimport]

I am trying to fix a few typos in the Java codes while I am reading the codes / javadocs.

Reporter: Bo Meng / @bomeng
Assignee: Bo Meng / @bomeng

PRs and other links:

• GitHub Pull Request #2076

_{Note: This issue was originally created as ARROW-2630. Please see the migration documentation for further details.}

[asfimport]

Bo Meng / @bomeng:
I will provide the pull request shortly.

[asfimport]

Bryan Cutler / @BryanCutler:
Issue resolved by pull request 2076
#2076