meson: bump minimum version to 0.55

This is now sufficient for the oldest supported Debian and Ubuntu
releases, and lets us assume dependency('foo') is sufficient for falling
back to foo.wrap.

Fixes Meson warning:

    WARNING: Project specifies a minimum meson_version '>=0.50' but uses features which were added in newer versions:
     * 0.54.0: {'fallback arg in dependency'}

Author: bgilbert

meson.build

@@ -9,7 +9,7 @@ project(
     'buildtype=debugoptimized',
   ],
   license : 'MIT',
-  meson_version : '>=0.50',
+  meson_version : '>=0.55',
   version : '1.2.0'
 )
 if not meson.is_subproject()
@@ -82,15 +82,11 @@ if found_uthash
 else
   # fall back to dependency() rather than subproject() so
   # --wrap-mode=nofallback works
-  uthash = dependency(
-    'uthash',
-    fallback : ['uthash', 'uthash_dep'],
-  )
+  uthash = dependency('uthash')
 endif
 if get_option('tests')
   check = dependency(
     'check',
-    fallback : ['check', 'check_dep'],
     version : '>=0.9.6',
   )
 endif
@@ -192,9 +188,7 @@ libdicom_dep = declare_dependency(
   include_directories : [library_includes, include_directories('.')],
   link_with : libdicom,
 )
-if meson.version().version_compare('>=0.54')
-  meson.override_dependency('libdicom', libdicom_dep)
-endif
+meson.override_dependency('libdicom', libdicom_dep)
 
 # tools
 executable(