Remove redundant dependency: bytestring-builder (#214)

It's not needed on GHC 7.8+ and we are already requiring 7.10+

websockets.cabal

@@ -91,7 +91,6 @@ Library
     base64-bytestring >= 0.1    && < 1.3,
     binary            >= 0.8.1  && < 0.11,
     bytestring        >= 0.9    && < 0.12,
-    bytestring-builder             < 0.11,
     case-insensitive  >= 0.3    && < 1.3,
     clock             >= 0.8    && < 0.9,
     containers        >= 0.3    && < 0.7,
@@ -151,7 +150,6 @@ Test-suite websockets-tests
     base64-bytestring >= 0.1    && < 1.3,
     binary            >= 0.8.1  && < 0.11,
     bytestring        >= 0.9    && < 0.12,
-    bytestring-builder             < 0.11,
     case-insensitive  >= 0.3    && < 1.3,
     clock             >= 0.8    && < 0.9,
     containers        >= 0.3    && < 0.7,
@@ -192,7 +190,6 @@ Executable websockets-client-example
     network,
     mtl
 
-
 Executable websockets-autobahn
   If !flag(Example)
     Buildable: False
@@ -214,7 +211,6 @@ Executable websockets-autobahn
     base64-bytestring >= 0.1    && < 1.3,
     binary            >= 0.8.1  && < 0.11,
     bytestring        >= 0.9    && < 0.12,
-    bytestring-builder             < 0.11,
     case-insensitive  >= 0.3    && < 1.3,
     clock             >= 0.8    && < 0.9,
     containers        >= 0.3    && < 0.7,
@@ -243,7 +239,6 @@ Benchmark bench-mask
     base64-bytestring >= 0.1    && < 1.3,
     binary            >= 0.8.1  && < 0.11,
     bytestring        >= 0.9    && < 0.12,
-    bytestring-builder             < 0.11,
     case-insensitive  >= 0.3    && < 1.3,
     clock             >= 0.8    && < 0.9,
     containers        >= 0.3    && < 0.7,