Allow yaml 0.9

Builds fine and all tests pass.

Author: felixonmars

stylish-haskell.cabal

@@ -60,7 +60,7 @@ Library
     mtl              >= 2.0    && < 2.3,
     semigroups       >= 0.18   && < 0.19,
     syb              >= 0.3    && < 0.8,
-    yaml             >= 0.7    && < 0.9
+    yaml             >= 0.7    && < 0.10
 
 Executable stylish-haskell
   Ghc-options:    -Wall
@@ -82,7 +82,7 @@ Executable stylish-haskell
     haskell-src-exts >= 1.18   && < 1.21,
     mtl              >= 2.0    && < 2.3,
     syb              >= 0.3    && < 0.8,
-    yaml             >= 0.7    && < 0.9
+    yaml             >= 0.7    && < 0.10
 
 Test-suite stylish-haskell-tests
   Ghc-options:    -Wall
@@ -131,7 +131,7 @@ Test-suite stylish-haskell-tests
     haskell-src-exts >= 1.18   && < 1.21,
     mtl              >= 2.0    && < 2.3,
     syb              >= 0.3    && < 0.8,
-    yaml             >= 0.7    && < 0.9
+    yaml             >= 0.7    && < 0.10
 
 Source-repository head
   Type:     git