allow use on non-OSX

.travis.yml

@@ -3,6 +3,7 @@ os: osx
 osx_image: xcode7.3
 julia:
     - 0.6
+    - 0.7
     - nightly
 notifications:
     email: false

deps/build.jl

@@ -1,2 +1,4 @@
-using Homebrew
-Homebrew.update()
+@static if VERSION < v"0.7-" ? is_apple() : Sys.isapple()
+    using Homebrew
+    Homebrew.update()
+end

src/Homebrew.jl

@@ -34,11 +34,23 @@ need is downloaded/installed, then calls `update_env()` to set the environment
 properly so that packages being installed can find their binaries.
 """
 function __init__()
-    # Let's see if Homebrew is installed.  If not, let's do that first!
-    (isdir(brew_prefix) && isdir(tappath)) || install_brew()
-
-    # Update environment variables such as PATH, DL_LOAD_PATH, etc...
-    update_env()
+    if VERSION < v"0.7-" ? is_apple() : Sys.isapple()
+        # Let's see if Homebrew is installed.  If not, let's do that first!
+        (isdir(brew_prefix) && isdir(tappath)) || install_brew()
+
+        # Update environment variables such as PATH, DL_LOAD_PATH, etc...
+        update_env()
+    else
+        # change this to an error in future
+        warning("""
+Homebrew.jl can only be used on Apple macOS. Suggested usage is
+
+    @static if Sys.isapple()
+        using Homebrew
+        # Homebrew specific code goes here
+    end
+""")
+    end
 end