Fix line number anchors in gitweb links.

In one case, provide a commit hash so that the line number is relative
to a known commit of the file. I found the commit in bridgedb.git where
the URL was added, then found a commit in torspec.git that was around
the same time and seems to point to the right place.

Subtract one from the line numbers; maybe the old gitweb and the new are
off by one relative to each other.

lib/bridgedb/Bridges.py

@@ -63,7 +63,7 @@ class BridgeRingParameters(object):
     :ivar list needFlags: List of two-tuples of desired flags_ assigned to a
         Bridge by the Bridge DirAuth.
 
-    .. _flags: https://gitweb.torproject.org/torspec.git/tree/dir-spec.txt#n1696
+    .. _flags: https://gitweb.torproject.org/torspec.git/tree/dir-spec.txt?id=6b557594ef#n1695
     """
 
     def __init__(self, needPorts=[], needFlags=[]):

lib/bridgedb/bridges.py

@@ -109,7 +109,7 @@ def update(self, flags):
           |      "Valid" if the router has been 'validated'.
 
         .. _dir-spec.txt:
-            https://gitweb.torproject.org/torspec.git/tree/dir-spec.txt?id=7647f6d4d#n1603
+            https://gitweb.torproject.org/torspec.git/tree/dir-spec.txt?id=7647f6d4d#n1602
 
         :param list flags: A list of strings containing each of the flags
             parsed from the 's'-line.