[stdlib] Fix typos in Dictionary.swift

Hi, I fixed several typos in Dictionary.swift file(#Line: 347, 1194).

- origin comments
```swift
// #347
// Prints "The 'star' image is a glyph.")

// #1194
// Prints "No value found for that key.""
```

- changed comments
```swift
// #347
// Prints "The 'star' image is a glyph.")  // I thought the ' ) ' character was unnecessary, so I removed it.

// #1194
// Prints "No value found for that key.""  // I thought the ' " ' character was unnecessary, so I removed it.
```

Author: Benjp-h

stdlib/public/core/Dictionary.swift

@@ -344,7 +344,7 @@
 ///     } else {
 ///         print("No glyphs found!")
 ///     }
-///     // Prints "The 'star' image is a glyph.")
+///     // Prints "The 'star' image is a glyph."
 ///
 /// Note that in this example, `imagePaths` is subscripted using a dictionary
 /// index. Unlike the key-based subscript, the index-based subscript returns
@@ -1191,7 +1191,7 @@ extension Dictionary {
   ///     } else {
   ///         print("No value found for that key.")
   ///     }
-  ///     // Prints "No value found for that key.""
+  ///     // Prints "No value found for that key."
   ///
   /// - Parameter key: The key to remove along with its associated value.
   /// - Returns: The value that was removed, or `nil` if the key was not