Update HTTP -> HTTPS

URLs updated to use HTTPS protocol where appropriate to improve security and privacy.

Author: Ronald Eddy Jr

CODING_STYLE.md

@@ -236,7 +236,7 @@ Example:
 #include <numeric>
 ```
 
-See [this issue](http://stackoverflow.com/questions/614302/c-header-order/614333#614333 "C header order") for the reason: this makes it easier to find missing includes in header files.
+See [this issue](https://stackoverflow.com/questions/614302/c-header-order/614333#614333 "C header order") for the reason: this makes it easier to find missing includes in header files.
 
 ## 13. Recommended reading
 

CONTRIBUTING.md

@@ -1,5 +1,5 @@
 # Contribution Guidelines
 
-Please see our contribution guidelines in [the Solidity documentation](http://solidity.readthedocs.io/en/latest/contributing.html).
+Please see our contribution guidelines in [the Solidity documentation](https://solidity.readthedocs.io/en/latest/contributing.html).
 
 Thank you for your help!