fix: add study tag to in-memory

Author: eottabom

posts/etc/in-memory.mdx

@@ -1,7 +1,7 @@
 ---
 title: "In Memory Database vs In Memory Data Grid"
 date: "2020-05-23"
-tags: ["Etc"]
+tags: ["Etc", "Study"]
 summary: "Comparison of In Memory Database and In Memory Data Grid"
 description: "In Memory Database와 In Memory Data Grid에 대해서 알아보자."
 ---