Code chunk and typo fixes to Environments.rmd

* Typo fix: changed "can be also" to "can also be"
* Typo fix: changed "determins" to "determines"
* Typo fix: removed extra "will"
* Typo fix: inserted a needed "are"
* Several similar code chunk fixes: Several code chunk outputs should be /<environment: R_GlobalEnv> instead of something like /<environment: 0x1034b3268>. So changed {r} to {r, eval = FALSE} and then manually entered desired output.

I assign the copyright of this contribution to Hadley Wickham.
Merge pull request #202 from liangcj/patch-3

Code chunk and typo fixes to Environments.rmd