fix combined_json for versions >0.3.10

[trocher]

What I did

Fixed the combined_json output for versions 0.4.x
Fixes #28

How I did it

pop from the dict version as it would be before the contract's data.

How to verify it

import vvm
print(vvm.compile_source("# pragma version 0.4.0", vyper_version="0.4.0"))

would return before:

{'<stdin>': '0.4.0'}

and now:

{'<stdin>': {'bytecode': '0x61000361000f6000396100036000f35f5ffd84038000a1657679706572830004000011', 'bytecode_runtime': '0x5f5ffd', 'blueprint_bytecode': '0x6100263d81600a3d39f3fe710061000361000f6000396100036000f35f5ffd84038000a1657679706572830004000011', 'abi': [], 'layout': {}, 'source_map': {'breakpoints': [], 'error_map': {'17': 'fallback function'}, 'pc_breakpoints': [], 'pc_jump_map': {'0': '-', '15': '-'}, 'pc_pos_map_compressed': '0:22:0:-;-1:-1:-1;-1:-1:-1;-1:-1:-1;-1:-1:-1;-1:-1:-1;-1:-1:-1;-1:-1:-1;-1:-1:-1;-1:-1:-1;-1:-1:-1;-1:-1:-1;-1:-1:-1;-1:-1:-1;-1:-1:-1;-1:-1:-1:-;-1:-1:-1;-1:-1:-1', 'pc_pos_map': {'0': [1, 0, 1, 22]}, 'pc_ast_map': {'0': [0, 0]}, 'pc_ast_map_item_keys': ['source_id', 'node_id']}, 'source_map_runtime': {'breakpoints': [], 'error_map': {'2': 'fallback function'}, 'pc_breakpoints': [], 'pc_jump_map': {'0': '-'}, 'pc_pos_map_compressed': '0:22:0:-;-1:-1:-1;-1:-1:-1', 'pc_pos_map': {'0': [1, 0, 1, 22]}, 'pc_ast_map': {'0': [0, 0]}, 'pc_ast_map_item_keys': ['source_id', 'node_id']}, 'method_identifiers': {}, 'userdoc': {}, 'devdoc': {}}}

Checklist

• I have confirmed that my PR passes all linting checks
• I have included test cases
• I have updated the documentation (README.md)
• I have added an entry to the changelog

[charles-cooper]

thanks!