adding mafft version 7.526

There's a new version of mafft!

I am unsure what has changed (this version isn't in https://mafft.cbrc.jp/alignment/software/changelog.html), but I imagine it's feature improvements and bug fixes.

I just copied the files from version 7.510 and updated the version ARG.

$ diff mafft/7.52{0,6}/Dockerfile
5c5
< ARG MAFFT_VER="7.520"
---
> ARG MAFFT_VER="7.526"

Pull Request (PR) checklist:

[X] Include a description of what is in this pull request in this message.
[x] The dockerfile successfully builds to a test target for the user creating the PR. (i.e. docker build --tag samtools:1.15test --target test docker-builds/samtools/1.15 )
[x] Directory structure as name of the tool in lower case with special characters removed with a subdirectory of the version number (i.e. spades/3.12.0/Dockerfile)
- [x] (optional) All test files are located in same directory as the Dockerfile (i.e. shigatyper/2.0.1/test.sh)
[x] Create a simple container-specific README.md in the same directory as the Dockerfile (i.e. spades/3.12.0/README.md)
- [x] If this README is longer than 30 lines, there is an explanation as to why more detail was needed
[x] Dockerfile includes the recommended LABELS
[x] Main README.md has been updated to include the tool and/or version of the dockerfile(s) in this PR
[x] Program_Licenses.md contains the tool(s) used in this PR and has been updated for any missing

StaPH-B / docker-builds