More naturally sort requirements.

pre_commit_hooks/requirements_txt_fixer.py

diff --git a/pre_commit_hooks/requirements_txt_fixer.py b/pre_commit_hooks/requirements_txt_fixer.py
index 2dec6bf..cc09242 100644
--- a/pre_commit_hooks/requirements_txt_fixer.py
+++ b/pre_commit_hooks/requirements_txt_fixer.py
@@ -18,7 +18,10 @@
         elif requirement.value == b'\n':
             return False
         else:
-            return self.value < requirement.value
+            return (
+                self.value.partition(b'==') <
+                requirement.value.partition(b'==')
+            )
 
 
 def fix_requirements(f):

tests/requirements_txt_fixer_test.py

diff --git a/tests/requirements_txt_fixer_test.py b/tests/requirements_txt_fixer_test.py
index b135fdf..3eac637 100644
--- a/tests/requirements_txt_fixer_test.py
+++ b/tests/requirements_txt_fixer_test.py
@@ -15,6 +15,7 @@
     (b'#comment\n\nbar\nfoo\n', 0, b'#comment\n\nbar\nfoo\n'),
     (b'\nfoo\nbar\n', 1, b'bar\n\nfoo\n'),
     (b'\nbar\nfoo\n', 0, b'\nbar\nfoo\n'),
+    (b'pyramid==1\npyramid-foo==2\n', 0, b'pyramid==1\npyramid-foo==2\n'),
 )