Fix typos/editing issues after #4061

Author: Blaisorblade

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -885,7 +885,7 @@ class Definitions {
    */
   def isImplicitFunctionClass(cls: Symbol) = scalaClassName(cls).isImplicitFunction
 
-  /** Is an ghost function class.
+  /** Is a ghost function class.
    *   - GhostFunctionN for N > 0
    *   - GhostImplicitFunctionN for N > 0
    */

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -781,7 +781,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
       }
       app match {
         case Apply(fun, args) if fun.tpe.widen.isGhostMethod =>
-          tpd.cpy.Apply(app)(fun = fun, args = args.map(arg => normalizeGhostExpr(arg, "This argument is given to an ghost parameter. ")))
+          tpd.cpy.Apply(app)(fun = fun, args = args.map(arg => normalizeGhostExpr(arg, "This argument is given to a ghost parameter. ")))
         case _ => app
       }
     }