running drender in RStudio does not show any error message from during 'docker build'

[behrica]

I just get a message in rstudio about 'the input device is not a TTY'

Removing intermediate container b970dc4754af
Successfully built 719f65c357fb
the input device is not a TTY
Error response from daemon: No such container: liftr_container_c2452cb0_af05_4540_84e3_1d794916ae40
Error response from daemon: No such container: liftr_container_c2452cb0_af05_4540_84e3_1d794916ae40
Untagged: 2016-10-13-food-consumption-tutorial:latest
Deleted: sha256:719f65c357fb7b95f1a9f96efaf54be223deca0ddeb503bfe4f44e5cd949d68c
Deleted: sha256:abec59b1a952cfbbbff3948226c36a34e19cb6f3f2b385e2f7e1723afca8d047
Deleted: sha256:8619cf17acd3d9a853baa8cb64411d3db48d94623e2456c1169b5946e8dc8ac5
Deleted: sha256:c6bb527ab7ea67bcf4ff9193b28751e69a68fcf440652e465dcd2f75064239f2
Deleted: sha256:a0ef05d4b8f3d460713785452b44a0533ebe5cb5e235be16c11b5e7aa7ce513f
Deleted: sha256:5ff9db48458dd83dfa4d3c5b2c7b86dcd49a734c2bdfb49c0397a245c9c0b695
Deleted: sha256:595523380493a5e987bba97cc77438935a0546c5d24cd84bc318474a20ee7e32
Deleted: sha256:22d1784df1a5d29a4976db682db6ca15353da5f9754653cdc59be7fd70eb559b
Deleted: sha256:2978b8fa064ea5ebeb87374c816a869461f65ad19c69d3e78c47a2c17761fd5b

this makes debugging problems very hard.
In a R session in a normal terminal it works, and the error mesage is visible, which was in my case a missing library:

processing file: 2016-10-13-food-consumption-tutorial.Rmd
  |.                                                                |   2%
   inline R code fragments

  |...                                                              |   4%
label: setup (with options) 
List of 1
 $ include: logi FALSE

  |....                                                             |   6%
  ordinary text without R code

  |......                                                           |   9%
label: unnamed-chunk-1
  |.......                                                          |  11%
  ordinary text without R code

  |........                                                         |  13%
label: unnamed-chunk-2
Quitting from lines 68-71 (2016-10-13-food-consumption-tutorial.Rmd) 
Error in library(sparklyr) : there is no package called 'sparklyr'

Running it in rstudio supresses basically the complete output of knitr.

[behrica]

I debugged this a noticed that this problem in rstudio disappers, if we remove the '-t' flag from 'docker run ...".
I think we neither need '-i' nor '-t' here, as the docker run in drender never executes a interactive shell.
I'll send a PR accordingly.