Fix issue with bias component in _v() (pattern.text)

This fixes a bug introduced in dc85534 which causes the majority of unit tests in pattern.en (test_en.py) to fail.
Resolves #182.

pattern/text/__init__.py

@@ -445,7 +445,7 @@ def f(v, *s):
         p = ("", "") if not p else (p[0] or "", p[1] or "")
         n = ("", "") if not n else (n[0] or "", n[1] or "")
         v = {}
-        f(v,  "b", " ")         # Bias.
+        f(v,  "b", "b")         # Bias.
         f(v,  "h", token[:1])   # Capitalization.
         f(v,  "w", token[-6:] if token not in self.known or token in self.unknown else "")
         f(v,  "x", token[-3:])  # Word suffix.