run R using English language

[pedro-andrade-inpe]

When RServer is initialised, set the language to language by running the following command:

Sys.setenv(LANG="en")

Using it, it is possible to avoid the problems in the continuous integration server such as:

Testing evaluate
Error in ...1ed53267c6a40e0101157cb54a/rstats/tests/basic/RServe.lua:202: Test expected:
  "[RServe] Error: objeto 'v' não encontrado"
  got:
  "[RServe] Error: object 'v' not found"
It would accept an error of at most 1 character(s), but got 13.
Error in ...1ed53267c6a40e0101157cb54a/rstats/tests/basic/RServe.lua:207: Test expected:
  "[RServe] Warning: a condição tem comprimento > 1 e somente o primeiro elemento será usado"
  got:
  "[RServe] Warning: the condition has length > 1 and only the first element will be used"
It would accept an error of at most 1 character(s), but got 47.

Translate the tests to english.