Fix typo in Design Pastebin.com exercise (#210)

Author: fabriziocucci

solutions/system_design/pastebin/README.md

@@ -126,7 +126,7 @@ To generate the unique url, we could:
     * Alternatively, we could also take the MD5 hash of randomly-generated data
 * [**Base 62**](https://www.kerstner.at/2012/07/shortening-strings-using-base-62-encoding/) encode the MD5 hash
     * Base 62 encodes to `[a-zA-Z0-9]` which works well for urls, eliminating the need for escaping special characters
-    * There is only one hash result for the original input and and Base 62 is deterministic (no randomness involved)
+    * There is only one hash result for the original input and Base 62 is deterministic (no randomness involved)
     * Base 64 is another popular encoding but provides issues for urls because of the additional `+` and `/` characters
     * The following [Base 62 pseudocode](http://stackoverflow.com/questions/742013/how-to-code-a-url-shortener) runs in O(k) time where k is the number of digits = 7: