[zanata/zanata-platform] 750bc3: chore(ZNTA-1735): update yarn version

[GitHub]

  Branch: refs/heads/ZNTA-1735-editorglossary
  Home:   https://github.com/zanata/zanata-platform
  Commit: 750bc385f0e22093f89a7563e50ed682f75fac10
      https://github.com/zanata/zanata-platform/commit/750bc385f0e22093f89a7563e50ed682f75fac10
  Author: David Mason <drdmason at gmail.com>
  Date:   2017-04-11 (Tue, 11 Apr 2017)

  Changed paths:
    M server/zanata-frontend/pom.xml

  Log Message:
  -----------
  chore(ZNTA-1735): update yarn version

Yarn seems to hang on Jenkins upon linking dependencies. Updating
to a version that works on my machine in case that helps.