Add ConnectionFactoryProvider.getDriver() implementation

getDriver() returns the driver identifier postgresql.

[resolves pgjdbc#77]

Author: mp911de

src/main/java/io/r2dbc/postgresql/PostgresqlConnectionFactoryProvider.java

@@ -98,4 +98,9 @@ public boolean supports(ConnectionFactoryOptions connectionFactoryOptions) {
 
         return true;
     }
+
+    @Override
+    public String getDriver() {
+        return POSTGRESQL_DRIVER;
+    }
 }

src/test/java/io/r2dbc/postgresql/PostgresqlConnectionFactoryProviderTest.java

@@ -102,4 +102,9 @@ void supports() {
             .option(USER, "test-user")
             .build())).isTrue();
     }
-}
+
+    @Test
+    void returnsDriverIdentifier() {
+        assertThat(this.provider.getDriver()).isEqualTo(POSTGRESQL_DRIVER);
+    }
+}