Update tests.

docs/contracts/abstract-contracts.rst

@@ -14,7 +14,7 @@ provided (no implementation body ``{ }`` was given).::
 
     pragma solidity >=0.4.0 <0.7.0;
 
-    contract Feline {
+    abstract contract Feline {
         function utterance() public returns (bytes32);
     }
 
@@ -23,7 +23,7 @@ all defined functions. The usage of an abstract contract as a base class is show
 
     pragma solidity >=0.4.0 <0.7.0;
 
-    contract Feline {
+    abstract contract Feline {
         function utterance() public returns (bytes32);
     }
 

docs/contracts/inheritance.rst

@@ -52,12 +52,12 @@ Details are given in the following example.
     // interface known to the compiler. Note the function
     // without body. If a contract does not implement all
     // functions it can only be used as an interface.
-    contract Config {
+    abstract contract Config {
         function lookup(uint id) public returns (address adr);
     }
 
 
-    contract NameReg {
+    abstract contract NameReg {
         function register(bytes32 name) public;
         function unregister() public;
     }