Use English as default locale for flagr instead of Chinese

[lawrenceong]

Description

As the contents for flagr is in English, set the default locale for
ElementUI to English (instead of defaulting to Chinese). This is to
prevent certain contents from being displayed in Chinese. eg. when
there are no flags available.

Motivation and Context

Keep the language consistent in the application.

How Has This Been Tested?

Launch the default flagr and run it using docker:

Before the change, confirm that the bug is present by launching a docker container as such:

docker run -p 18000:18000 checkr/flagr

Visit the GUI and delete all flags. You will see No Data in Chinese written as 暂无数据.

Test the change and launch a docker container with the change. You will see No Data.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-io]

Codecov Report

Merging #226 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #226   +/-   ##
=======================================
  Coverage   83.87%   83.87%           
=======================================
  Files          24       24           
  Lines        1433     1433           
=======================================
  Hits         1202     1202           
  Misses        174      174           
  Partials       57       57

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[zhouzhuojie]

Thanks! LGTM