Fix: typo README.md (#404)

topics/databases/README.md

@@ -20,7 +20,7 @@
 
 Relational (SQL)
 NoSQL
-Time serties
+Time series
 </b></details>
 
 ### SQL
@@ -188,4 +188,4 @@ A database designed specifically for time series based data.
 It comes with multiple optimizations:
 
 <TODO>: complete this :)
-</b></details>
+</b></details>