Fixing instructions by correcting instruction to (#1877)

> openzeppelin-solidity@2.3.0 lint /home/luiserebii/github/openzeppelin-solidity
> npm run lint:js && npm run lint:sol

> openzeppelin-solidity@2.3.0 lint:js /home/luiserebii/github/openzeppelin-solidity
> eslint .

> openzeppelin-solidity@2.3.0 lint:sol /home/luiserebii/github/openzeppelin-solidity
> solhint --max-warnings 0 "contracts/**/*.sol", alongside some minor grammatical corrections

CONTRIBUTING.md

@@ -29,7 +29,7 @@ NOTE: The directory `openzeppelin-contracts` represents your fork's local copy.
 git checkout -b fix/some-bug-#123
 ```
 
-3) Make your changes, add your files, commit and push to your fork.
+3) Make your changes, add your files, commit, and push to your fork.
 
 ```
 git add SomeFile.js
@@ -37,11 +37,11 @@ git commit "Fix some bug #123"
 git push origin fix/some-bug-#123
 ```
 
-4) Run tests, linter etc. It can be done by running local continuous integration and make sure it pass
+4) Run tests, linter, etc. This can be done by running local continuous integration and make sure it passes.
 
 ```bash
 npm test
-npm linter
+npm run lint
 ```
 
 or you can simply run CircleCI locally
@@ -54,7 +54,7 @@ circleci local execute --job test
 5) Go to [github.com/OpenZeppelin/openzeppelin-contracts](https://github.com/OpenZeppelin/openzeppelin-contracts) in your web browser and issue a new pull request.
 
 *IMPORTANT* Read the PR template very carefully and make sure to follow all the instructions. These instructions
-refer to some very important conditions that your PR must meet in order to be accepted, such as making sure that all tests pass, JS linting tests pass, solidity linting tests pass, etc.
+refer to some very important conditions that your PR must meet in order to be accepted, such as making sure that all tests pass, JS linting tests pass, Solidity linting tests pass, etc.
 
 6) Maintainers will review your code and possibly ask for changes before your code is pulled in to the main repository. We'll check that all tests pass, review the coding style, and check for general code correctness. If everything is OK, we'll merge your pull request and your code will be part of OpenZeppelin.
 
@@ -62,7 +62,7 @@ refer to some very important conditions that your PR must meet in order to be ac
 
 ## All set!
 
-If you have any questions feel free to post them to github.com/OpenZeppelin/openzeppelin-contracts/issues.
+If you have any questions, feel free to post them to github.com/OpenZeppelin/openzeppelin-contracts/issues.
 
 Finally, if you're looking to collaborate and want to find easy tasks to start, look at the issues we marked as ["Good first issue"](https://github.com/OpenZeppelin/openzeppelin-contracts/labels/good%20first%20issue).