Fix typos

Rakefile

@@ -152,7 +152,7 @@ def download_from_url(libname, lib_path, file_name, sha256sum_expected, url)
       else
         puts 'Check sha256sum'
         v = check_sha256sum(lib_path, sha256sum_expected)
-        retrun false unless v
+        return false unless v
       end
 
       puts "Copying #{lib_path} to #{target_path}"

examples/basic_table.rb

@@ -20,7 +20,7 @@
 # Protects BlockCaller objects from garbage collection.
 @block_callers = []
 def rbcallback(*args, &block)
-  args << [0] if args.size == 1 # Argument types are ommited
+  args << [0] if args.size == 1 # Argument types are omitted
   block_caller = Fiddle::Closure::BlockCaller.new(*args, &block)
   @block_callers << block_caller
   block_caller

examples/basic_table_image.rb

@@ -34,7 +34,7 @@
 # Protects BlockCaller objects from garbage collection.
 @block_callers = []
 def rbcallback(*args, &block)
-  args << [0] if args.size == 1 # Argument types are ommited
+  args << [0] if args.size == 1 # Argument types are omitted
   block_caller = Fiddle::Closure::BlockCaller.new(*args, &block)
   @block_callers << block_caller
   block_caller

lib/libui.rb

@@ -59,7 +59,7 @@ def window_position(w)
     end
 
     # FIXME: This is a workaround for a old version of Fiddle.
-    # Fiddle 1.1.2 and above should be able to handle one charactor string.
+    # Fiddle 1.1.2 and above should be able to handle one character string.
     # See https://github.com/ruby/fiddle/issues/96
 
     def open_type_features_add(otf, a, b, c, d, value)