Bump middleman from 4.3.0.rc.4 to 4.3.1

Bumps [middleman](https://github.com/middleman/middleman) from 4.3.0.rc.4 to 4.3.1.
- [Release notes](https://github.com/middleman/middleman/releases)
- [Changelog](https://github.com/middleman/middleman/blob/v4.3.1/CHANGELOG.md)
- [Commits](middleman/middleman@v4.3.0.rc.4...v4.3.1)

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -1,7 +1,7 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    activesupport (5.1.6.1)
+    activesupport (5.0.7.1)
       concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (>= 0.7, < 2)
       minitest (~> 5.1)
@@ -22,14 +22,15 @@ GEM
     coffee-script-source (1.12.2)
     colorize (0.8.1)
     concurrent-ruby (1.1.4)
-    contracts (0.16.0)
+    contracts (0.13.0)
     dotenv (2.6.0)
     erubis (2.7.0)
     ethon (0.11.0)
       ffi (>= 1.3.0)
     execjs (2.7.0)
+    fast_blank (1.0.0)
     fastimage (2.1.5)
-    ffi (1.10.0)
+    ffi (1.9.25)
     haml (5.0.4)
       temple (>= 0.8.0)
       tilt
@@ -48,47 +49,46 @@ GEM
     i18n (0.9.5)
       concurrent-ruby (~> 1.0)
     kramdown (1.17.0)
-    listen (3.1.5)
+    listen (3.0.8)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
-      ruby_dep (~> 1.2)
     memoist (0.16.0)
     mercenary (0.3.6)
-    middleman (4.3.0.rc.4)
+    middleman (4.3.1)
       coffee-script (~> 2.2)
       haml (>= 4.0.5)
       kramdown (~> 1.2)
-      middleman-cli (= 4.3.0.rc.4)
-      middleman-core (= 4.3.0.rc.4)
-      sass (>= 3.4.0, < 4.0)
+      middleman-cli (= 4.3.1)
+      middleman-core (= 4.3.1)
     middleman-aria_current (0.1.1)
       middleman-core (~> 4.0)
     middleman-autoprefixer (2.10.0)
       autoprefixer-rails (>= 9.1.4)
       middleman-core (>= 3.3.3)
-    middleman-cli (4.3.0.rc.4)
+    middleman-cli (4.3.1)
       thor (>= 0.17.0, < 2.0)
-    middleman-core (4.3.0.rc.4)
-      activesupport (>= 4.2, < 5.2)
+    middleman-core (4.3.1)
+      activesupport (>= 4.2, < 5.1)
       addressable (~> 2.3)
-      backports (~> 3.11)
-      bundler (~> 1.1)
-      contracts (~> 0.16.0)
+      backports (~> 3.6)
+      bundler
+      contracts (~> 0.13.0)
       dotenv
       erubis
       execjs (~> 2.0)
+      fast_blank
       fastimage (~> 2.0)
       hamster (~> 3.0)
       hashie (~> 3.4)
-      i18n (~> 0.7)
-      listen (~> 3.0)
+      i18n (~> 0.9.0)
+      listen (~> 3.0.0)
       memoist (~> 0.14)
       padrino-helpers (~> 0.13.0)
       parallel
       rack (>= 1.4.5, < 3)
-      sass (>= 3.4)
+      sassc (~> 2.0)
       servolux
-      tilt (~> 2.0)
+      tilt (~> 2.0.9)
       uglifier (~> 3.0)
     middleman-data_source (0.8.1)
       borrower (~> 0.9)
@@ -115,17 +115,20 @@ GEM
     rack (2.0.6)
     rack-test (0.6.3)
       rack (>= 1.0)
+    rake (12.3.2)
     rb-fsevent (0.10.3)
     rb-inotify (0.10.0)
       ffi (~> 1.0)
     redcarpet (3.4.0)
     rouge (2.2.1)
-    ruby_dep (1.5.0)
     sass (3.7.3)
       sass-listen (~> 4.0.0)
     sass-listen (4.0.0)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
+    sassc (2.0.0)
+      ffi (~> 1.9.6)
+      rake
     servolux (0.13.0)
     temple (0.8.0)
     thor (0.20.3)