Fix typos in GRADLE_PLUGIN.md & INTEROP.md (#649)

* Fix typo in GRADLE_PLUGIN.md

* Fix typo in INTEROP.md

GRADLE_PLUGIN.md

@@ -111,7 +111,7 @@ cinterop execution (see the `dumpParameters` task in `samles/csvparser/build.gra
              apiVersion 'version'
 
              // Native interop to use in the artifact.
-             useInerop "interopName"
+             useInterop "interopName"
         }
      }
 

INTEROP.md

@@ -51,7 +51,7 @@ Write something to console and watch server echoing it back.
 Structurally it's a simple property file, looking like this:
 
 
-    header = zlib.h
+    headers = zlib.h
     compilerOpts = -std=c99
 
 Then run `cinterop` tool with something like (note that for host libraries not included