fix typos in md files

Author: etpinard

.github/PULL_REQUEST_TEMPLATE.md

@@ -15,7 +15,7 @@ Developers are strongly encouraged to first make a PR to their own plotly.js for
 Before opening a pull request, developer should: 
 
 - `git rebase` their local branch off the latest `master`,
-- make sure to **not** `git add` the `dist/` folder (the `dist/` is updated only on verion bumps),
+- make sure to **not** `git add` the `dist/` folder (the `dist/` is updated only on version bumps),
 - write an overview of what the PR attempts to do,
 - select the _Allow edits from maintainers_ option (see this [article](https://help.github.com/articles/allowing-changes-to-a-pull-request-branch-created-from-a-fork/) for more details).
 

CONTRIBUTING.md

@@ -24,14 +24,14 @@ We use the following [labels](https://github.com/plotly/plotly.js/labels) to tra
 | `type: community` | issue left open for community input and pull requests |
 | `type: duplicate` | *self-explanatory* |
 | `type: wontfix` | *self-explanatory* |
-| `status: discussion needed` | Issue or PR that required discussion among maintaners before moving forward |
-| `status: in progress` | PRs that required some intial feedback but not ready to merge |
+| `status: discussion needed` | Issue or PR that required discussion among maintainers before moving forward |
+| `status: in progress` | PRs that required some initial feedback but not ready to merge |
 | `status: reviewable` | PRs that are completed from the author's perspective |
 | `status: on hold` | PRs that are put on hold |
 
 ## Development
 
-#### Perequisites
+#### Prerequisites
 
 - git
 - [node.js](https://nodejs.org/en/). We recommend using node.js v6.x or v4.x (both LTS).