Bump strong_migrations from 0.6.1 to 0.6.8

[dependabot-preview[bot]]

Bumps strong_migrations from 0.6.1 to 0.6.8.

Changelog

Sourced from strong_migrations's changelog.

0.6.8 (2020-05-13)

• change_column_null on a column with a NOT NULL constraint is safe in Postgres 12+

0.6.7 (2020-05-13)

• Improved comments in initializer
• Fixed string timeouts for Postgres

0.6.6 (2020-05-08)

• Added warnings for missing and long lock timeouts
• Added install generator

0.6.5 (2020-05-06)

• Fixed deprecation warnings with Ruby 2.7

0.6.4 (2020-04-16)

• Added check for add_reference with foreign_key: true

0.6.3 (2020-04-04)

• Increasing precision of decimal or numeric column is safe in Postgres 9.2+
• Making decimal or numeric column unconstrained is safe in Postgres 9.2+
• Changing between timestamp and timestamptz when session time zone is UTC in Postgres 12+
• Increasing the length of a varchar column from under 255 up to 255 in MySQL and MariaDB
• Increasing the length of a varchar column over 255 in MySQL and MariaDB

0.6.2 (2020-02-03)

• Fixed PostgreSQL version check

Commits

• f095d6e Version bump to 0.6.8 [skip ci]
• a633d53 Added change_column_null before Postgres 12
• d231b32 Updated validate constraint code for Postgres 12+
• 7b67113 Added change_column_null update to readme [skip ci]
• 6e0069b Quote as recommended in instructions - shouldn't matter, but likely more common
• 4accf60 change_column_null on a column with a NOT NULL constraint is safe in Postgres...
• e86a21f Removed outdated comment [skip ci]
• 81557d4 Better variable name [skip ci]
• 4c3cba1 Version bump to 0.6.7 [skip ci]
• 659056e Better comment [skip ci]
• Additional commits viewable in compare view

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[dependabot-preview[bot]]

Superseded by #152.