Correct documentation of blob8/buf8 read/write-(u)bits

The write-* methods are available on buf8, not blob8. Also correct
the version in which they were added, 2019.01 did not come out.

Author: taboege

doc/Type/Blob.pod6

@@ -402,7 +402,7 @@ Defined as:
 Returns a native C<num> value for the B<eight> bytes starting at the given
 position.
 
-=head1 Methods on blob8 only (6.d, 2019.01 and later)
+=head1 Methods on blob8 only (6.d, 2019.03 and later)
 
 =head2 method read-ubits
 

doc/Type/Buf.pod6

@@ -316,13 +316,13 @@ Writes a native C<num64> IEEE floating point value at the given position with
 the given endianness.
 
 
-=head1 Methods on blob8 only (6.d, 2019.01 and later)
+=head1 Methods on buf8 only (6.d, 2019.03 and later)
 
 =head2 method write-ubits
 
 Defined as:
 
-    method write-ubits(blob8:D: uint $pos, uint $bits, UInt:D $value --> Nil)
+    method write-ubits(buf8:D: uint $pos, uint $bits, UInt:D $value --> Nil)
 
 Writes an unsigned integer value to the B<bits> from the given B<bit> offset
 and given number of bits.  The endianness of the bits is assumed to be
@@ -332,7 +332,7 @@ C<BigEndian>.  Always returns Nil.
 
 Defined as:
 
-    method write-bits(blob8:D: uint $pos, uint $bits, Int:D $value --> Nil)
+    method write-bits(buf8:D: uint $pos, uint $bits, Int:D $value --> Nil)
 
 Writes a signed integer value for the B<bits> from the given B<bit> offset
 and given number of bits.  The endianness of the bits is assumed to be