Update pragma versions for 0.6.0

docs/contracts/abstract-contracts.rst

@@ -22,7 +22,7 @@ provided (no implementation body ``{ }`` was given).::
 Such abstract contracts can not be instantiated directly. This is also true, if an abstract contract itself does implement
 all defined functions. The usage of an abstract contract as a base class is shown in the following example::
 
-    pragma solidity >=0.4.0 <0.7.0;
+    pragma solidity ^0.6.0;
 
     abstract contract Feline {
         function utterance() public virtual returns (bytes32);

docs/contracts/functions.rst

@@ -280,7 +280,7 @@ Below you can see an example of a Sink contract that uses function ``receive``.
 
 ::
 
-    pragma solidity >=0.5.0 <0.7.0;
+    pragma solidity ^0.6.0;
 
     // This contract keeps all Ether sent to it with no way
     // to get it back.
@@ -335,7 +335,7 @@ operations as long as there is enough gas passed on to it.
 
 ::
 
-    pragma solidity >=0.5.0 <0.7.0;
+    pragma solidity ^0.6.0;
 
     contract Test {
         // This function is called for all messages sent to

docs/contracts/inheritance.rst

@@ -38,7 +38,7 @@ Details are given in the following example.
 
 ::
 
-    pragma solidity >=0.5.0 <0.7.0;
+    pragma solidity ^0.6.0;
 
 
     contract Owned {
@@ -125,7 +125,7 @@ Note that above, we call ``mortal.kill()`` to "forward" the
 destruction request. The way this is done is problematic, as
 seen in the following example::
 
-    pragma solidity >=0.4.22 <0.7.0;
+    pragma solidity ^0.6.0;
 
     contract owned {
         constructor() public { owner = msg.sender; }

docs/control-structures.rst

@@ -567,7 +567,7 @@ A failure in an external call can be caught using a try/catch statement, as foll
 
 ::
 
-    pragma solidity >=0.5.0 <0.7.0;
+    pragma solidity ^0.6.0;
 
     interface DataFeed { function getData(address token) external returns (uint value); }
 

docs/security-considerations.rst

@@ -211,7 +211,7 @@ Now someone tricks you into sending ether to the address of this attack wallet:
 
 ::
 
-    pragma solidity >=0.5.0 <0.7.0;
+    pragma solidity ^0.6.0;
 
     interface TxUserWallet {
         function transferTo(address payable dest, uint amount) external;

docs/style-guide.rst

@@ -89,7 +89,7 @@ Blank lines may be omitted between groups of related one-liners (such as stub fu
 
 Yes::
 
-    pragma solidity >=0.4.0 <0.7.0;
+    pragma solidity ^0.6.0;
 
     abstract contract A {
         function spam() public virtual pure;
@@ -290,7 +290,7 @@ Within a grouping, place the ``view`` and ``pure`` functions last.
 
 Yes::
 
-    pragma solidity >=0.4.0 <0.7.0;
+    pragma solidity ^0.6.0;
 
     contract A {
         constructor() public {