Bump combine_pdf from 1.0.26 to 1.0.31

Bumps [combine_pdf](https://github.com/boazsegev/combine_pdf) from 1.0.26 to 1.0.31.
- [Release notes](https://github.com/boazsegev/combine_pdf/releases)
- [Changelog](https://github.com/boazsegev/combine_pdf/blob/master/CHANGELOG.md)
- [Commits](https://github.com/boazsegev/combine_pdf/compare/v1.0.26...v1.0.31)

---
updated-dependencies:
- dependency-name: combine_pdf
  dependency-version: 1.0.31
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -245,7 +245,7 @@ GEM
       coffee-script-source
       execjs
     coffee-script-source (1.12.2)
-    combine_pdf (1.0.26)
+    combine_pdf (1.0.31)
       matrix
       ruby-rc4 (>= 0.1.5)
     concurrent-ruby (1.3.5)
@@ -477,7 +477,7 @@ GEM
       net-pop
       net-smtp
     marcel (1.1.0)
-    matrix (0.4.2)
+    matrix (0.4.3)
     method_source (1.1.0)
     mime-types (3.7.0)
       logger