docs: bump install snippets to vortex 0.4.0

README and tutorial both showed the previous v0.3.2 Maven coordinates;
0.4.0 is now live on Maven Central.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: dfa1

README.md

@@ -27,7 +27,7 @@ for zero-copy memory-mapped reads.
 <dependency>
   <groupId>io.github.dfa1.vortex</groupId>
   <artifactId>vortex-reader</artifactId>
-  <version>0.3.2</version>
+  <version>0.4.0</version>
 </dependency>
 ```
 

docs/tutorial.md

@@ -26,7 +26,7 @@ Add the dependency to `pom.xml` (inside `<dependencies>`):
 <dependency>
   <groupId>io.github.dfa1.vortex</groupId>
   <artifactId>vortex-reader</artifactId>
-  <version>0.3.2</version>
+  <version>0.4.0</version>
 </dependency>
 ```