[Documentation] Add missing forward slash in two places

Author: aciidgh

Sources/PackageDescription4/PackageDependency.swift

@@ -50,7 +50,7 @@ extension Package.Dependency {
     }
 
     /// Add a package dependency starting with a specific minimum version, up to
-    // but not including a specific maximum version.
+    /// but not including a specific maximum version.
     ///
     /// For example
     ///

Sources/PackageDescription4/Target.swift

@@ -160,7 +160,7 @@ public final class Target {
     }
 
     /// Create a library or executable target.
-    //
+    ///
     /// A target can either contain Swift or C-family source files. You cannot
     /// mix Swift and C-family source files within a target. A target is
     /// considered to be an executable target if there is a `main.swift`,
@@ -196,7 +196,7 @@ public final class Target {
     }
 
     /// Create a library or executable target.
-    //
+    ///
     /// A target can either contain Swift or C-family source files. You cannot
     /// mix Swift and C-family source files within a target. A target is
     /// considered to be an executable target if there is a `main.swift`,