Switch to new noqa syntax for flake8 3.0

Apparently, `# noqa ignore=X` worked before, but now the syntax is more terse,
like this: `# noqa: X`.

See the changelog here:
http://flake8.pycqa.org/en/latest/release-notes/3.0.0.html

beets/library.py

@@ -40,7 +40,7 @@ import beets
 # `memoryview`, depending on the Python version, tells it that we
 # actually mean non-text data.
 if six.PY2:
-    BLOB_TYPE = buffer  # noqa ignore=F821
+    BLOB_TYPE = buffer  # noqa: F821
 else:
     BLOB_TYPE = memoryview
 

beets/util/__init__.py

@@ -658,9 +658,10 @@ def as_string(value):
     """Convert a value to a Unicode object for matching with a query.
     None becomes the empty string. Bytestrings are silently decoded.
     """
-    buffer_types = memoryview
     if six.PY2:
-        buffer_types = (buffer, memoryview)  # noqa ignore=F821
+        buffer_types = buffer, memoryview  # noqa: F821
+    else:
+        buffer_types = memoryview
 
     if value is None:
         return u''

beets/util/confit.py

@@ -44,9 +44,9 @@ REDACTED_TOMBSTONE = 'REDACTED'
 # Utilities.
 
 PY3 = sys.version_info[0] == 3
-STRING = str if PY3 else unicode  # noqa ignore=F821
-BASESTRING = str if PY3 else basestring  # noqa ignore=F821
-NUMERIC_TYPES = (int, float) if PY3 else (int, float, long)  # noqa ignore=F821
+STRING = str if PY3 else unicode  # noqa: F821
+BASESTRING = str if PY3 else basestring  # noqa: F821
+NUMERIC_TYPES = (int, float) if PY3 else (int, float, long)  # noqa: F821
 
 
 def iter_first(sequence):

beetsplug/bpd/gstplayer.py

@@ -30,7 +30,7 @@ from beets import ui
 
 import gi
 gi.require_version('Gst', '1.0')
-from gi.repository import GLib, Gst  # noqa ignore=E402
+from gi.repository import GLib, Gst  # noqa: E402
 
 
 Gst.init(None)