Update manifest-reference.md

LKedward · milancurcic · web-flow · commit d407ee0b992d · 2021-04-14T17:46:34.000+01:00
Co-authored-by: Milan Curcic &lt;caomaco@gmail.com&gt;
diff --git a/manifest-reference.md b/manifest-reference.md
@@ -364,7 +364,7 @@ specify the module name using the *external-modules* key in the *build* table.
 
 ```toml
 [build]
-external-modules = "netcdff"
+external-modules = "netcdf"
 ```
 
 Multiple external modules can be specified as a list.
