Drop support for GHC < 8.2

gtk2hs-buildtools fails to build with GHC < 8.2.

Author: maoe

.travis.yml

@@ -42,12 +42,6 @@ jobs:
     - compiler: ghc-8.2.2
       addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.2.2","cabal-install-3.0","libgtk2.0-dev"]}}
       os: linux
-    - compiler: ghc-8.0.2
-      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.0.2","cabal-install-3.0","libgtk2.0-dev"]}}
-      os: linux
-    - compiler: ghc-7.10.2
-      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-7.10.2","cabal-install-3.0","libgtk2.0-dev"]}}
-      os: linux
     - compiler: ghc-8.8.1
       addons: {"homebrew": {"packages":["gtk+", "gtk-mac-integration"]}}
       env: PKG_CONFIG_PATH=/usr/local/opt/libffi/lib/pkgconfig

threadscope.cabal

@@ -35,9 +35,7 @@ Cabal-version:       >= 1.6
 Data-files:          threadscope.ui, threadscope.png
 Extra-source-files:  include/windows_cconv.h
                      README.md
-Tested-with:         GHC == 7.10.2
-                     GHC == 8.0.2
-                     GHC == 8.2.2
+Tested-with:         GHC == 8.2.2
                      GHC == 8.4.4
                      GHC == 8.6.5
                      GHC == 8.8.1
@@ -48,7 +46,7 @@ source-repository head
 
 Executable threadscope
   Main-is:           Main.hs
-  Build-Depends:     base >= 4.6 && < 5,
+  Build-Depends:     base >= 4.10 && < 5,
                      gtk >= 0.12 && < 0.16,
                      cairo < 0.14,
                      glib < 0.14,