DOC: add `source activate` for older versions of Anaconda and fix a typo
In the contrib docs, `conda activate` should be `source activate`, and there was also an extraneous period after the "continuous integration" heading.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19282?src=pr&el=h1) Report
> Merging [#19282](https://codecov.io/gh/pandas-dev/pandas/pull/19282?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/4086e420c8c7a5f72fb9090a7d2d97045cf443bb?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19282/graphs/tree.svg?token=eZ4WkYLtcO&width=650&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/19282?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #19282   +/-   ##
=======================================
  Coverage   91.54%   91.54%           
=======================================
  Files         148      148           
  Lines       48870    48870           
=======================================
  Hits        44737    44737           
  Misses       4133     4133
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.91% <ø> (ø)` | :arrow_up: |
| #single | `41.66% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19282?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19282?src=pr&el=footer). Last update [4086e42...7c1e95d](https://codecov.io/gh/pandas-dev/pandas/pull/19282?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
