[Docs] Use NOTE: for cop docs

The sections marked as `NOTE` on docs.rubocop.org have been updated.
Sections where changing to `NOTE:` does not require special interpretation remain as `Note:`.

lib/rubocop/cop/layout/heredoc_indentation.rb

@@ -6,7 +6,7 @@ module Layout
       # Checks the indentation of the here document bodies. The bodies
       # are indented one step.
       #
-      # Note: When ``Layout/LineLength``'s `AllowHeredoc` is false (not default),
+      # NOTE: When ``Layout/LineLength``'s `AllowHeredoc` is false (not default),
       #       this cop does not add any offenses for long here documents to
       #       avoid ``Layout/LineLength``'s offenses.
       #

lib/rubocop/cop/style/quoted_symbols.rb

@@ -9,7 +9,7 @@ module Style
       #
       # String interpolation is always kept in double quotes.
       #
-      # Note: `Lint/SymbolConversion` can be used in parallel to ensure that symbols
+      # NOTE: `Lint/SymbolConversion` can be used in parallel to ensure that symbols
       # are not quoted that don't need to be. This cop is for configuring the quoting
       # style to use for symbols that require quotes.
       #

lib/rubocop/cop/style/redundant_file_extension_in_require.rb

@@ -6,7 +6,7 @@ module Style
       # Checks for the presence of superfluous `.rb` extension in
       # the filename provided to `require` and `require_relative`.
       #
-      # Note: If the extension is omitted, Ruby tries adding '.rb', '.so',
+      # NOTE: If the extension is omitted, Ruby tries adding '.rb', '.so',
       #       and so on to the name until found. If the file named cannot be found,
       #       a `LoadError` will be raised.
       #       There is an edge case where `foo.so` file is loaded instead of a `LoadError`