我正在尝试使用composer更新我的symfony依赖关系，但出现错误。
我尝试使用composer.phar更新，但似乎无法正常工作。
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.
Problem 1
- Conclusion: don't install symfony/symfony v3.4.20
- Conclusion: don't install symfony/symfony v3.4.19
- Conclusion: don't install symfony/symfony v3.4.18
- Conclusion: remove symfony/symfony v3.4.17
- Conclusion: don't install symfony/symfony v3.4.17
- Conclusion: don't install symfony/symfony v3.4.16
- Conclusion: don't install symfony/symfony v3.4.15
- Conclusion: don't install symfony/symfony v3.4.14
- Conclusion: don't install symfony/symfony v3.4.13
- Conclusion: don't install symfony/symfony v3.4.12
- Conclusion: don't install symfony/symfony v3.4.11
- Conclusion: don't install symfony/symfony v3.4.10
- Conclusion: don't install symfony/symfony v3.4.9
- Conclusion: don't install symfony/symfony v3.4.8
- Conclusion: don't install symfony/symfony v3.4.7
- Conclusion: don't install symfony/symfony v3.4.6
- Conclusion: don't install symfony/symfony v3.4.5
- Conclusion: don't install symfony/symfony v3.4.4
- Conclusion: don't install symfony/symfony v3.4.3
- Conclusion: don't install symfony/symfony v3.4.2
- Conclusion: don't install symfony/symfony v3.4.1|install symfony/symfony v3.4.2
- don't install symfony/templating v3.4.2|don't install symfony/symfony v3.4.0
- don't install symfony/symfony v3.4.0|remove symfony/templating v3.4.2
- Installation request for symfony/symfony 3.4.* -> satisfiable by symfony/symfony[v3.4.0, v3.4.1, v3.4.10, v3.4.11, v3.4.12, v3.4.13, v3.4.14, v3.4.15, v3.4.16, v3.4.17, v3.4.18, v3.4.19, v3.4.2, v3.4.20, v3.4.3, v3.4.4, v3.4.5, v3.4.6, v3.4.7, v3.4.8, v3.4.9].
- Installation request for symfony/templating v3.4.2 -> satisfiable by symfony/symfony[v3.4.2], symfony/templating[v3.4.2].
有人有想法吗？ 谢谢 ！