Fix typos: missing type in method signature

Author: mernst

checker-qual/src/main/java/org/checkerframework/checker/index/qual/IndexFor.java

@@ -19,7 +19,7 @@
  *
  * <pre>{@code
  * class String {
- *   char charAt(@IndexFor("this") index) { ... }
+ *   char charAt(@IndexFor("this") int index) { ... }
  * }
  * }</pre>
  *

docs/manual/index-checker.tex

@@ -124,7 +124,7 @@
 
   \begin{Verbatim}
   class String {
-    char charAt(@IndexFor("this") index) { ... }
+    char charAt(@IndexFor("this") int index) { ... }
   }
   \end{Verbatim}