Fix spelling

ehuss · ehuss · commit 2e9ec3a0d0d3 · 2019-01-27T09:26:07.000-08:00
diff --git a/src/macros.md b/src/macros.md
@@ -1,6 +1,6 @@
 # Macros
 
-The functionality and syntax of Rust can be extended with custom definitons
+The functionality and syntax of Rust can be extended with custom definitions
 called macros. They are given names, and invoked through a consistent
 syntax:`some_extension!(...)`.
 
