Update custom_preprocessors.rs

Author: Dylan-DPC

tests/custom_preprocessors.rs

@@ -36,7 +36,7 @@ fn ask_the_preprocessor_to_blow_up() {
     let dummy_book = DummyBook::new();
     let temp = dummy_book.build().unwrap();
     let mut md = MDBook::load(temp.path()).unwrap();
-    md.with_preprecessor(example());
+    md.with_preprocessor(example());
 
     md.config
         .set("preprocessor.nop-preprocessor.blow-up", true)
@@ -52,7 +52,7 @@ fn process_the_dummy_book() {
     let dummy_book = DummyBook::new();
     let temp = dummy_book.build().unwrap();
     let mut md = MDBook::load(temp.path()).unwrap();
-    md.with_preprecessor(example());
+    md.with_preprocessor(example());
 
     md.build().unwrap();
 }