Fix grammar

Author: zohairawan

src/packaging/jar_files.md

@@ -6,7 +6,7 @@ are just ZIP files with a few special bits of "metadata."
 ZIP files are a common way of bundling a bunch of files up into one file.[^compression]
 
 You don't need to know exactly where this metadata goes or what all of it is for yet,
-just that at a high level its all just files in a ZIP.
+just that at a high level it's all just files in a ZIP.
 
 [^compression]: This bundling up also generally includes "compression," where
 the single file might be smaller than the combined sizes of its components. Most people don't