fix typo

Signed-off-by: Katherine Shen <[email protected]>

data-prepper-plugins/date-processor/src/main/java/org/opensearch/dataprepper/plugins/processor/date/DateProcessorConfig.java

@@ -201,7 +201,7 @@ public static boolean isValidPattern(final String pattern) {
     @JsonPropertyDescription("Specifies under what condition the <code>date</code> processor should run. " +
             "Default is no condition.")
     @ExampleValues({
-        @Example(value = "/some_key == null", description = "The processor will only run when on events where this condition evaluates to true.")
+        @Example(value = "/some_key == null", description = "The processor will only run on events where this condition evaluates to true.")
     })
     private String dateWhen;