Fix version pragma in documentation.

docs/control-structures.rst

@@ -279,7 +279,7 @@ groupings of expressions.
 
 ::
 
-    pragma solidity >0.4.23 <0.5.0;
+    pragma solidity >0.4.23 <0.6.0;
 
     contract C {
         uint[] data;

docs/frequently-asked-questions.rst

@@ -173,7 +173,7 @@ situation.
 
 If you do not want to throw, you can return a pair::
 
-    pragma solidity >0.4.23 <0.5.0;
+    pragma solidity >0.4.23 <0.6.0;
 
     contract C {
         uint[] counters;

docs/solidity-by-example.rst

@@ -389,7 +389,7 @@ high or low invalid bids.
 
 ::
 
-    pragma solidity >0.4.23 <0.5.0;
+    pragma solidity >0.4.23 <0.6.0;
 
     contract BlindAuction {
         struct Bid {